EXHIBIT 4.1

                          REGISTRATION RIGHTS AGREEMENT

     REGISTRATION RIGHTS AGREEMENT (this "AGREEMENT"), dated as of October 6,
2005, by and among La Jolla Pharmaceutical Company, a Delaware corporation (the
"COMPANY"), and the undersigned Purchasers (individually a "PURCHASER" and
collectively the "PURCHASERS").

                              PRELIMINARY STATEMENT

     A. In connection with the Securities Purchase Agreement by and among the
parties hereto of even date herewith (the "SECURITIES PURCHASE AGREEMENT"), the
Company has agreed, upon the terms and subject to the conditions of the
Securities Purchase Agreement, to issue and sell to the Purchasers (i) shares
(the "COMMON SHARES") of the Company's common stock, par value $0.01 per share
(the "COMMON STOCK") and (ii) "Contingent Warrants" and "Closing Warrants" (each
as defined in the Securities Purchase Agreement) to purchase shares of Common
Stock (the "WARRANTS" and, as exercised, the "WARRANT SHARES").

     B. To induce the Purchasers to execute and deliver the Securities Purchase
Agreement, the Company has agreed to provide certain registration rights under
the Securities Act of 1933, as amended, and the rules and regulations
thereunder, or any similar successor statute (collectively, the "SECURITIES
ACT"), and applicable state securities laws.

     NOW, THEREFORE, in consideration of the premises and the mutual covenants
contained herein and other good and valuable consideration, the receipt and
sufficiency of which are hereby acknowledged, the Company and each of the
Purchasers hereby agree as follows:

1.   DEFINITIONS.

     As used in this Agreement, the following terms shall have the following
meanings:

     (a) "DELAY PAYMENT RATE" means (i) during the first two weeks of a Damages
Accrual Period, an amount per week (or portion thereof) per share of Common
Stock equal to 0.5% of the Per Share Purchase Price (as defined in the
Securities Purchase Agreement) of such share, (ii) during the next two weeks of
a Damages Accrual Period, an amount per week (or portion thereof) per share of
Common Stock equal to 1% of the Per Share Purchase Price of such share, and
(iii) during the remainder of a Damages Accrual Period, an amount per week (or
portion thereof) per share of Common Stock equal to 2% of the Per Share Purchase
Price of such share.

     (b) "INVESTOR" means a Purchaser and any transferee or assignee thereof to
whom a Purchaser assigns its rights under this Agreement and who agrees to
become bound by the provisions of this Agreement in accordance with Section 9.

     (c) "PERSON" means a corporation, a limited liability company, an
association, a partnership, an organization, a business, an individual, a
governmental or political subdivision thereof or a governmental agency.

     (d) "REGISTER," "REGISTERED," and "REGISTRATION" refer to a registration
effected by preparing and filing one or more Registration Statements (as defined
below) in compliance with the Securities Act and pursuant to Rule 415 under the
Securities Act or any successor rule providing for offering securities on a
continuous or delayed basis ("RULE 415"), and the declaration or ordering of
effectiveness of such Registration Statement(s) by the United States Securities
and Exchange Commission (the "SEC").

     (e) "REGISTRABLE SECURITIES" means (i) the Common Shares issued or issuable
pursuant to the terms of the Securities Purchase Agreement, (ii) the Warrant
Shares issued or issuable upon exercise of the Warrants, (iii) any shares of
capital stock issued or issuable with respect to the Common Shares and the
Warrant Shares as a result of any stock split, stock dividend, recapitalization,
exchange or similar event or otherwise, without regard to any limitations on the
issuance of the Common Shares or exercise of the Warrants and (iv) any
securities of the Company issued upon the reclassification of any of the
foregoing.

     (f) "REGISTRATION DELAY" means the occurrence of any of (i) a Registration
Statement covering all the Registrable Securities (other than, if the Share
Authorization Approval is not obtained prior to the closing of the transactions
contemplated by the Securities Purchase Agreement, any Warrant Shares for which
the Share Authorization Approval is required prior to their issuance) is not
filed with the SEC on or before the Filing Deadline or is not declared effective
by the SEC on or before the Effectiveness Deadline, (ii) if the Share
Authorization Approval is not obtained prior to the closing of the transactions
contemplated by the Securities Purchase Agreement, a Registration Statement
covering all the Warrant Shares for which the Share Authorization Approval is
required prior to their issuance is not filed with the SEC on or before the
Warrant Share Filing Deadline or is not declared effective by the SEC on or
before the Warrant Share Effectiveness Deadline, (iii) a Registration Statement
in connection with a Demand Registration covering all of the Registrable
Securities required to be covered thereby is not filed with the SEC on or before
the deadline described in the last sentence of Section 2(b) or is not declared
effective by the SEC on or before the deadline described in the last sentence of
Section 2(b), (iv) on any day during the Registration Period (other than during
an Allowable Grace Period, as defined in Section 3(g)), any Registrable Security
required to be included in such Registration Statement cannot be sold pursuant
to such Registration Statement as a matter of law or because the Company has
failed to perform its obligations under this Agreement within the applicable
time period required for such performance (including, without limitation,
because of a failure to keep such Registration Statement effective, to disclose
such information as is necessary for sales to be made pursuant to such
Registration Statement or to register a sufficient number of shares of Common
Stock), or (v) a Grace Period (as defined in Section 3(g)) exceeds the length of
an Allowable Grace Period.

     (g) "REGISTRATION STATEMENT" means a registration statement or registration
statements of the Company filed under the Securities Act covering the
Registrable Securities.


                                        2

     (h) "WARRANT TRIGGER DATE" means the date at which the Contingent Warrants
become exercisable in accordance with the terms thereof.

2.   REGISTRATION.

     (a) Mandatory Registration.

          (i) The Company shall prepare, and, as soon as practicable, but in no
event later than forty-five (45) days after the earlier of (A) the Closing Date
(as defined in the Securities Purchase Agreement) or (B) the Warrant Trigger
Date (the earlier of such dates, the "FILING DEADLINE"), file with the SEC a
Registration Statement or Registration Statements (as necessary) on Form S-3
covering the resale of all of the Registrable Securities (other than, if the
Share Authorization Approval is not obtained prior to the closing of the
transactions contemplated by the Securities Purchase Agreement, any Warrant
Shares for which the Share Authorization Approval is required prior to their
issuance). In the event that Form S-3 is unavailable for such a registration,
the Company shall use such other form as is available for such a registration,
subject to the provisions of Section 2(f). The Company shall use its best
efforts to cause such Registration Statement to be declared effective by the SEC
as soon as possible, but in no event later than the earlier of (a) the fifth
business day after the SEC advises the Company that either (A) it will not
review such Registration Statement or (B) it has no further comments with
respect to such Registration Statement, and (b) one hundred thirty five (135)
days after the Closing Date (the earlier of such dates, the "EFFECTIVENESS
DEADLINE").

          (ii) , If the Share Authorization Approval is not obtained prior to
the closing of the transactions contemplated by the Securities Purchase
Agreement, the Company shall prepare, and, as soon as practicable, but in no
event later than the later of (A) the Filing Deadline and (B) fifteen days (15)
days after the date on which the Share Authorization Approval is obtained (the
"WARRANT SHARE FILING DEADLINE"), file with the SEC a Registration Statement or
Registration Statements (as necessary) on Form S-3 covering the resale of all of
the Warrant Shares for which the Share Authorization Approval is required prior
to their issuance. In the event that Form S-3 is unavailable for such a
registration, the Company shall use such other form as is available for such a
registration, subject to the provisions of Section 2(f). If the Share
Authorization Approval is not obtained prior to the closing of the transactions
contemplated by the Securities Purchase Agreement, the Company shall use its
best efforts to cause such Registration Statement to be declared effective by
the SEC as soon as possible, but in no event later than the earlier of (a) the
fifth business day after the SEC advises the Company that either (A) it will not
review such Registration Statement or (B) it has no further comments with
respect to such Registration Statement, and (b) ninety (90) days after the date
on which the Share Authorization Approval is obtained (the earlier of such
dates, the "WARRANT SHARE EFFECTIVENESS DEADLINE").

     (b) Demand Registrations. If for any reason prior to the expiration of the
Registration Period (as hereinafter defined), a Registration Statement required
to be filed pursuant to Section 2(a) ceases to be effective or fails to cover
all of the Registrable Securities required to be covered by such Registration
Statement, any Investors may on subsequently demand registration pursuant to the
terms of and within the time frames set forth in Section 2(a) by providing
written demand registration notice to the Company (a "DEMAND REGISTRATION").


                                        3

The Filing Deadline and Effectiveness Deadline with respect to any Demand
Registration will be those dates which are forty-five (45) days and one hundred
thirty five (135) days after the date that the Demand Registration notice is
delivered to the Company.

     (c) Piggy-Back Registrations. If at any time prior to the expiration of the
Registration Period (as hereinafter defined), the number of shares of Common
Stock available for sale under a Registration Statement is insufficient to cover
all of the Registrable Securities and the Company proposes to file with the SEC
a Registration Statement relating to an offering for its own account or the
account of others under the Securities Act of any of its securities (other than
on Form S-4, Form S-8 or Form S-1 (or their equivalents at such time) relating
to securities to be issued solely in connection with any acquisition of any
entity or business or to equity securities issuable in connection with stock
option or other employee benefit plans approved by the board of directors of the
Company) the Company shall promptly send to each Investor written notice of the
Company's intention to file a Registration Statement and of such Investor's
rights under this Section 2(c) and, if within twenty (20) days after receipt of
such notice, such Investor shall so request in writing, the Company shall
include in such Registration Statement all or any part of the Registrable
Securities such Investor requests to be registered, subject to the priorities
set forth in this Section 2(c) below. No right to registration of Registrable
Securities under this Section 2(c) shall be construed to limit any registration
required under Section 2(a). The obligations of the Company under this Section
2(c) may be waived by Investors holding a majority of the Registrable
Securities. If an offering in connection with which an Investor is entitled to
registration under this Section 2(c) is an underwritten offering, then each
Investor whose Registrable Securities are included in such Registration
Statement shall, unless otherwise agreed by the Company, offer and sell such
Registrable Securities in an underwritten offering using the same underwriter or
underwriters and, subject to the provisions of this Agreement, on the same terms
and conditions as other shares of Common Stock included in such underwritten
offering. If a registration pursuant to this Section 2(c) is to be an
underwritten public offering and the managing underwriter(s) advise the Company
in writing, that in their reasonable good faith opinion, marketing or other
factors dictate that a limitation on the number of shares of Common Stock which
may be included in the Registration Statement is necessary to facilitate and not
adversely affect the proposed offering, then the Company shall include in such
registration: (1) first, all securities the Company proposes to sell for its own
account and (2) second, up to the full number of securities proposed to be
registered for the account of the Investors entitled to registration under this
Section 2(c), pro rata among such Investors on the basis of the number of
Registrable Securities that each of them requested to be included in such
registration.

     (d) Allocation of Registrable Securities. The initial number of Registrable
Securities included in any Registration Statement and each increase in the
number of Registrable Securities included therein shall be allocated pro rata
among the Investors based on the number of Registrable Securities held by each
Investor at the time the Registration Statement covering such initial number of
Registrable Securities or increase thereof is declared effective by the SEC. In
the event that an Investor sells or otherwise transfers any of such Investor's
Registrable Securities, each transferee shall be allocated a pro rata portion of
the then remaining number of Registrable Securities included in such
Registration Statement for such transferor. Any shares of Common Stock included
in a Registration Statement and which remain allocated to any Person which
ceases to hold any Registrable Securities covered by such Registration Statement
shall be


                                        4

allocated to the remaining Investors, pro rata based on the number of
Registrable Securities then held by such Investors which are covered by such
Registration Statement.

     (e) Legal Counsel. Subject to Section 5 of this Agreement, the Investors
holding at least a majority of the Registrable Securities shall have the right
to select one legal counsel to review and comment upon any registration pursuant
to this Agreement ("LEGAL COUNSEL"), which shall be Baker & McKenzie LLP or such
other counsel as is thereafter designated by the holders of a majority of
Registrable Securities and of which the Company and its counsel have been given
prior notice. The Legal Counsel shall not represent any Investor that sends such
counsel written notice that such Investor does not wish such counsel to
represent it in connection with the matters discussed in this Section 2(e). The
Investors, other than any Investor that delivers the notice discussed in the
preceding sentence, hereby waive any conflict of interest or potential conflict
of interest that may arise as a result of the representation of such Investors
by the Legal Counsel in connection with the subject matter of this Agreement.
These provisions will not prohibit any other counsel to an Investor from
reviewing and commenting on any registration filed pursuant to this Agreement at
no cost to the Company. The Company shall reasonably cooperate with Legal
Counsel in performing the Company's obligations under this Agreement.

     (f) Ineligibility for Form S-3. In the event that Form S-3 is not available
for any registration of Registrable Securities hereunder, the Company shall (i)
register the sale of the Registrable Securities on another appropriate form
reasonably acceptable to the holders of a majority of the Registrable Securities
and (ii) undertake to register the Registrable Securities on Form S-3 as soon as
such form is available, provided that the Company shall maintain the
effectiveness of the Registration Statement then in effect until such time as a
Registration Statement on Form S-3 covering the Registrable Securities has been
declared effective by the SEC.

     (g) Failure to File, Obtain and Maintain Effectiveness of Registration
Statement. If a Registration Delay occurs the Company shall pay to each holder
of Registrable Securities (the "REGISTRATION DELAY PAYMENTS"), as liquidated
damages and not as a penalty, and calculated for each share of Common Stock for
which a Registration Statement is required to be filed pursuant to the terms of
Section 2(a) then outstanding that is a Registrable Security and not covered for
resale at such time pursuant to the terms of a Registration Statement, an
accruing amount per each such share equal to the Delay Payment Rate for each
week (or portion thereof) during the Damages Accrual Period; provided that such
Registration Delay Payments shall be paid only to the Investors that have
complied with their obligations under Section 4 of this Agreement with respect
thereto. The Registration Delay Payments shall accrue from the first day of the
applicable Registration Delay through the date it is cured (the "DAMAGES ACCRUAL
PERIOD"), and shall be payable in cash to the record holders of the Registrable
Securities entitled thereto on the last business day of each calendar month. The
parties agree that the sole monetary damages payable for a violation of the
terms of Section 2(a) shall be such liquidated damages (unless such liquidated
damages are disallowed, reduced or not permitted by applicable law). Nothing
shall preclude any Investor from pursuing or obtaining specific performance or
other equitable relief with respect to this Agreement in accordance with
applicable law. The parties hereto agree that the liquidated damages provided
for in this Section 2(g) constitute a reasonable estimate of the damages that
may be incurred by holders of Registrable Securities by reason of the failure of
the


                                        5

Registration Statement to be filed or declared effective or available for
effecting resales of Registrable Securities in accordance with the provisions
hereof.

3.   RELATED OBLIGATIONS.

     At such time as the Company is obligated to file a Registration Statement
with the SEC pursuant to Section 2(a), the Company will use its best efforts to
effect the registration of the Registrable Securities in accordance with the
intended method of distribution thereof and, pursuant thereto, the Company shall
have the following obligations:

     (a) The Company shall promptly prepare and file with the SEC a Registration
Statement with respect to the Registrable Securities (but in no event later than
the Filing Deadline or Warrant Share Filing Deadline, as applicable) and use its
best efforts to cause such Registration Statement relating to the Registrable
Securities to become effective as soon as practicable after such filing (but in
no event later than the applicable Effectiveness Deadline or Warrant Share
Effectiveness Deadline). The Company shall keep each Registration Statement
effective pursuant to Rule 415 at all times until the earlier of (i) the date as
of which all of the Investors may sell all of the Registrable Securities covered
by such Registration Statement without restriction pursuant to Rule 144(k)
promulgated under the Securities Act (or successor thereto) or (ii) the date on
which the Investors shall have sold all the Registrable Securities covered by
such Registration Statement either pursuant to the Registration Statement or in
one or more transactions in which the acquirer obtained unlegended certificates
representing the Registrable Securities so purchased (the "REGISTRATION
PERIOD"), which Registration Statement (including any amendments or supplements
thereto and prospectuses contained therein) shall not contain any untrue
statement of a material fact or omit to state a material fact required to be
stated therein, or necessary to make the statements therein (in the case of any
prospectus only, in light of the circumstances under which they were made) not
misleading.

     (b) The Company shall prepare and file with the SEC such amendments
(including post-effective amendments) and supplements to a Registration
Statement and the prospectus used in connection with such Registration
Statement, which prospectus is to be filed pursuant to Rule 424 promulgated
under the Securities Act, as may be necessary to keep such Registration
Statement effective at all times during the Registration Period, and, during
such period, comply with the provisions of the Securities Act with respect to
the disposition of all Registrable Securities of the Company covered by such
Registration Statement until such time as all of such Registrable Securities
shall have been disposed of in accordance with the intended methods of
distribution by the seller or sellers thereof as set forth in such Registration
Statement. In the case of amendments and supplements to a Registration Statement
which are required to be filed pursuant to this Agreement (including pursuant to
this Section 3(b)) by reason of the Company filing a report on Form 10-K, Form
10-Q or Form 8-K or any analogous report under the Securities Exchange Act of
1934, as amended (the "EXCHANGE ACT"), the Company shall have incorporated such
report by reference into the Registration Statement, if applicable, or shall
file such amendments or supplements with the SEC on the same day on which the
Exchange Act report is filed which created the requirement for the Company to
amend or supplement the Registration Statement.


                                        6

     (c) The Company shall (a) permit Legal Counsel and any legal counsel for a
particular Investor to review and comment upon those sections of (i) the
Registration Statement which are applicable to the Investors at least five (5)
business days prior to its filing with the SEC and (ii) all other Registration
Statements and all amendments and supplements to all Registration Statements
which are applicable to the Investors (except for Proxy Statements, Annual
Reports on Form 10-K, Quarterly Reports on Form 10-Q and Current Reports on Form
8-K and any similar or successor reports) within a reasonable number of days
prior to the their filing with the SEC and (b) not file any document in a form
to which Legal Counsel or such legal counsel reasonably objects. The Company
shall furnish to Legal Counsel, without charge, (i) any correspondence from the
SEC or the staff of the SEC to the Company or its representatives relating to
any Registration Statement, provided the Legal Counsel shall keep such
correspondence confidential and shall not provide copies thereof to any Investor
without the Investor's express prior written consent, (ii) promptly after the
same is prepared and filed with the SEC, one copy of any Registration Statement
and any amendment(s) thereto, including financial statements and schedules and
all exhibits and (iii) upon the effectiveness of any Registration Statement, one
copy of the prospectus included in such Registration Statement and all
amendments and supplements thereto. The Company shall reasonably cooperate with
Legal Counsel and such other legal counsel in performing the Company's
obligations pursuant to this Section 3.

     (d) The Company shall furnish to each Investor whose Registrable Securities
are included in any Registration Statement, without charge, (i) promptly after
the same is prepared and filed with the SEC, at least one copy of such
Registration Statement and any amendment(s) thereto, including financial
statements and schedules, and all exhibits and each preliminary prospectus, (ii)
upon the effectiveness of any Registration Statement, ten (10) copies of the
prospectus included in such Registration Statement and all amendments and
supplements thereto (or such other number of copies as such Investor may
reasonably request) and (iii) such other documents, including copies of any
preliminary or final prospectus, as such Investor may reasonably request from
time to time in order to facilitate the disposition of the Registrable
Securities owned by such Investor. From and after December 1, 2005, the Company
shall comply with the requirements of Rule 153 and 172 with respect to the
filing of a final prospectus with the SEC.

     (e) The Company shall use its best efforts to (i) register and qualify the
Registrable Securities covered by a Registration Statement under all other
securities or "blue sky" laws of such jurisdictions in the United States, (ii)
prepare and file in those jurisdictions, such amendments (including
post-effective amendments) and supplements to such registrations and
qualifications as may be necessary to maintain the effectiveness thereof during
the Registration Period, (iii) take such other actions as may be necessary to
maintain such registrations and qualifications in effect at all times during the
Registration Period, and (iv) take all other actions reasonably necessary or
advisable to qualify the Registrable Securities for sale in such jurisdictions;
provided, however, that the Company shall not be required in connection
therewith or as a condition thereto to (w) make any change in the Company's
Certificate of Incorporation or by-laws that the Company's board of directors
determines in good faith to be contrary to the best interests of the Company and
its shareholders, (x) qualify to do business in any jurisdiction where it would
not otherwise be required to qualify but for this Section 3(e), (y) subject
itself to general taxation in any such jurisdiction, or (z) file a general
consent to service of process in any


                                        7

such jurisdiction. The Company shall promptly notify Legal Counsel and each
Investor who holds Registrable Securities of the receipt by the Company of any
notification with respect to the suspension of the registration or qualification
of any of the Registrable Securities for sale under the securities or "blue sky"
laws of any jurisdiction in the United States or its receipt of actual notice of
the initiation or threat of any proceeding for such purpose.

     (f) As promptly as practicable after becoming aware of such event or
development, the Company shall notify Legal Counsel and each Investor in writing
of the happening of any event as a result of which the prospectus included in a
Registration Statement, as then in effect, includes an untrue statement of a
material fact or omission to state a material fact required to be stated therein
or necessary to make the statements therein, in light of the circumstances under
which they were made, not misleading, and promptly prepare a supplement or
amendment to such Registration Statement to correct such untrue statement or
omission, and deliver ten (10) copies of such supplement or amendment to Legal
Counsel and each Investor (or such other number of copies as Legal Counsel or
such Investor may reasonably request). The Company shall also promptly notify
Legal Counsel and each Investor in writing (i) when a prospectus or any
prospectus supplement or post-effective amendment has been filed, and when a
Registration Statement or any post-effective amendment has become effective
(notification of such effectiveness shall be delivered to Legal Counsel and each
Investor by facsimile on the same day of such effectiveness), (ii) of any
request by the SEC for amendments or supplements to a Registration Statement or
related prospectus or related information, and (iii) of the Company's reasonable
determination that a post-effective amendment to a Registration Statement would
be appropriate.

     (g) The Company shall use its best efforts to prevent the issuance of any
stop order or other suspension of effectiveness of a Registration Statement, or
the suspension of the qualification of any of the Registrable Securities for
sale in any jurisdiction and, if such an order or suspension is issued, to
obtain the withdrawal of such order or suspension at the earliest possible
moment and to notify Legal Counsel and each Investor who holds Registrable
Securities being sold of the issuance of such order and the resolution thereof
or its receipt of actual notice of the initiation or threat of any proceeding
for such purpose.

     (h) At the reasonable request of any Investor and at such Investor's
expense, the Company shall use its best efforts to furnish to such Investor, on
the date of the effectiveness of the Registration Statement and thereafter from
time to time on such dates as an Investor may reasonably request (i) a letter,
dated such date, from the Company's independent certified public accountants in
form and substance as is customarily given by independent certified public
accountants to underwriters in an underwritten public offering, and (ii) an
opinion, dated as of such date, of counsel representing the Company for purposes
of such Registration Statement, in form, scope and substance as is customarily
given in an underwritten public offering, addressed to the Investors.

     (i) The Company shall, upon reasonable notice and during normal business
hours, make available for inspection by (i) any Investor, (ii) Legal Counsel and
any other legal counsel representing an Investor and (iii) one firm of
accountants or other agents retained by the Investors (collectively, the
"INSPECTORS") all pertinent financial and other records, and pertinent corporate
documents and properties of the Company (collectively, the "RECORDS"), which are


                                        8

requested for any purpose reasonably related to the Investors' rights and/or the
Company's obligations under this Agreement, and cause the Company's officers,
directors and employees to supply all information which any Inspector may
reasonably request; provided, however, that each Inspector which is not a party
hereto shall agree in writing prior to obtaining access to any Records, and each
Investor hereby agrees, to hold in strict confidence and shall not make any
disclosure (except to an Investor similarly bound by the terms hereof) or use of
any Record or other information which the Company determines in good faith to be
confidential, and of which determination the Inspectors are so notified, unless
(a) the disclosure of such Records is necessary to avoid or correct a
misstatement or omission in any Registration Statement or is otherwise required
under the Securities Act, (b) the release of such Records is ordered pursuant to
a final, non-appealable subpoena or order from a court or government body of
competent jurisdiction, or (c) the information in such Records has been made
generally available to the public other than by disclosure in violation of this
or any other agreement of which the Inspector has knowledge. Neither the Company
nor any Inspector of a particular Investor shall provide any confidential
information to any other Investor unless such Investor is first informed of the
confidential nature of such information and given a reasonable opportunity to
determine whether to accept disclosure of such confidential information. The
Company shall not be required to disclose any confidential information in such
Records to any Inspector until and unless such Inspector shall have entered into
confidentiality agreements with the Company with respect thereto, substantially
in the form of this Section 3(i). Each Investor receiving the Records agrees
that it shall, if permitted by applicable law, upon learning that disclosure of
such Records is sought in or by a court or governmental body of competent
jurisdiction or through other means, give prompt notice to the Company prior to
making any such disclosure and allow the Company, at its expense, to undertake
appropriate action to prevent disclosure of, or to obtain a protective order
for, the Records deemed confidential. Each Investor undertaking an inspection
pursuant to this Section 3(i) shall, and shall instruct its other Inspectors to,
use commercially reasonable efforts to perform any such inspection in a manner
designed to not materially disrupt the business activities of the Company.

     (j) The Company shall hold in confidence and not make any disclosure of
information concerning an Investor provided to the Company unless (i) disclosure
of such information is necessary to comply with federal or state securities
laws, (ii) the disclosure of such information is necessary to avoid or correct a
misstatement or omission in any Registration Statement, (iii) the release of
such information is ordered pursuant to a subpoena or other final,
non-appealable order from a court or governmental body of competent
jurisdiction, (iv) such information has been made generally available to the
public other than by disclosure in violation of this Agreement or any other
agreement, or (v) such Investor consents to the form and content of any such
disclosure. The Company agrees that it shall, if permitted by applicable law,
upon learning that disclosure of such information concerning an Investor is
sought in or by a court or governmental body of competent jurisdiction or
through other means, give prompt written notice to such Investor prior to making
any such disclosure and allow such Investor, at the Investor's expense, to
undertake appropriate action to prevent disclosure of, or to obtain a protective
order for, such information.

     (k) The Company shall use its best efforts either to (i) cause all the
Registrable Securities covered by a Registration Statement to be listed on each
securities exchange on which securities of the same class or series issued by
the Company are then listed, if any, if the listing


                                        9

of such Registrable Securities is then permitted under the rules of such
exchange, or (ii) secure designation and quotation of all the Registrable
Securities covered by the Registration Statement on The NASDAQ Stock Market. The
Company shall pay all fees and expenses in connection with satisfying its
obligation under this Section 3(k).

     (l) The Company shall cooperate with the Investors who hold Registrable
Securities being offered and, to the extent applicable, to facilitate the timely
preparation and delivery of certificates (not bearing any restrictive legend)
representing the Registrable Securities to be offered pursuant to a Registration
Statement and enable such certificates to be in such denominations or amounts,
as the case may be, as the Investors may reasonably request and registered in
such names as the Investors may request.

     (m) The Company shall provide a transfer agent and registrar of all such
Registrable Securities not later than the effective date of such Registration
Statement.

     (n) If requested by an Investor, the Company shall (i) as soon as
practicable incorporate in a prospectus supplement or post-effective amendment,
as necessary, such information as an Investor requests to be included therein
relating to the Investor and the sale and distribution of Registrable
Securities, including, without limitation, information with respect to the
number of Registrable Securities being offered or sold, the purchase price being
paid therefor and any other terms of the offering of the Registrable Securities
to be sold in such offering; and (ii) as soon as practicable make all required
filings of such prospectus supplement or post-effective amendment after being
notified of the matters to be incorporated in such prospectus supplement or
post-effective amendment.

     (o) The Company shall use its best efforts to cause the Registrable
Securities covered by the applicable Registration Statement to be registered
with or approved by such other governmental agencies or authorities as may be
necessary to consummate the disposition of such Registrable Securities within
the United States.

     (p) The Company shall otherwise use its best efforts to comply with all
applicable rules and regulations of the SEC in connection with any registration
hereunder.

     (q) Within two (2) business days after a Registration Statement which
covers applicable Registrable Securities is ordered effective by the SEC, the
Company shall deliver, and shall cause legal counsel for the Company to deliver,
to the transfer agent for such Registrable Securities (with copies to the
Investors whose Registrable Securities are included in such Registration
Statement) confirmation that such Registration Statement has been declared
effective by the SEC.

     (r) Notwithstanding anything to the contrary in this Section 3, at any time
after the applicable Registration Statement has been declared effective by the
SEC, the Company may delay the disclosure of material non-public information
concerning the Company the disclosure of which at the time is not, in the good
faith opinion of the Board of Directors of the Company and its counsel, in the
best interest of the Company and, in the opinion of counsel to the Company,
otherwise required (a "GRACE PERIOD"); provided, that the Company shall promptly
(i) notify the Investors in writing of the existence of material non-public
information giving rise


                                       10

to a Grace Period (provided that in each notice the Company will not disclose
the content of such material non-public information to the Investors) and the
date on which the Grace Period will begin, and (ii) notify the Investors in
writing of the date on which the Grace Period ends; and, provided further, that
no Grace Periods shall exceed thirty (30) consecutive days and during any
consecutive three hundred sixty-five (365) day period, such Grace Periods shall
not exceed an aggregate of sixty (60) days (an "ALLOWABLE GRACE PERIOD"). For
purposes of determining the length of a Grace Period above, the Grace Period
shall begin on and include the date the holders receive the notice referred to
in clause (i) and shall end on and include the later of the date the holders
receive the notice referred to in clause (ii) and the date referred to in such
notice. The provisions of Section 3(g) hereof shall not be applicable during the
period of any Allowable Grace Period. Upon expiration of the Grace Period, the
Company shall again be bound by the first sentence of Section 3(f) with respect
to the information giving rise thereto unless such material non-public
information is no longer applicable.

4.   OBLIGATIONS OF THE INVESTORS.

     (a) At least seven (7) days prior to the first anticipated filing date of a
Registration Statement, the Company shall notify each Investor in writing of the
information the Company requires from each such Investor if such Investor elects
to have any of such Investor's Registrable Securities included in such
Registration Statement. It shall be a condition precedent to the obligations of
the Company to complete the registration pursuant to this Agreement with respect
to the Registrable Securities of a particular Investor that such Investor shall
furnish to the Company such information regarding itself, the Registrable
Securities held by it and the intended method of disposition of the Registrable
Securities held by it as shall be reasonably required to effect the registration
of such Registrable Securities and shall execute such documents in connection
with such registration as the Company may reasonably request, in each case
within ten (10) days of being notified by the Company of its necessity.

     (b) Each Investor by such Investor's acceptance of the Registrable
Securities agrees to cooperate with the Company as reasonably requested by the
Company in connection with the preparation and filing of any Registration
Statement hereunder, unless such Investor has notified the Company in writing of
such Investor's election to exclude all of such Investor's Registrable
Securities from such Registration Statement.

     (c) Each Investor agrees that, upon receipt of any notice from the Company
of the happening of any event of the kind described in Section 3(g) or the first
sentence of 3(f), such Investor will immediately discontinue disposition of
Registrable Securities pursuant to any Registration Statement(s) covering such
Registrable Securities until such Investor's receipt of the copies of the
supplemented or amended prospectus contemplated by Section 3(g) or the first
sentence of 3(f) or receipt of notice that no supplement or amendment is
required. Notwithstanding anything to the contrary, the Company shall cause its
transfer agent to deliver unlegended shares of Common Stock to a transferee of
an Investor in accordance with the terms of the Securities Purchase Agreement in
connection with any sale of Registrable Securities with respect to which an
Investor has entered into a contract for sale prior to the Investor's receipt of
a notice from the Company of the happening of any event of the kind described in
Section 3(g) or the first sentence of Section 3(f) and for which the Investor
has not yet settled.


                                       11

     (d) As promptly as practicable after becoming aware of such event, each
Investor shall notify the Company in writing of the happening of any event as a
result of which the information provided in writing by such Investor to the
Company expressly for use in the Prospectus included in a Registration
Statement, as then in effect, includes an untrue statement of a material fact or
omission to state a material fact required to be stated therein or necessary to
make the statements therein, in light of the circumstances under which they were
made, not misleading; provided, however, that no separate written notification
shall be required for any event disclosed by such Investor in a timely filing
with the SEC relating to the Company's securities.

5.   EXPENSES OF REGISTRATION.

     All expenses incurred in connection with registrations, filings or
qualifications pursuant to Sections 2 and 3 of this Agreement, including,
without limitation, all registration, listing and qualifications fees, printers
and accounting fees, transfer agent fees and fees and disbursements of counsel
for the Company, but excluding underwriting discounts and commissions, shall be
paid by the Company. The Company shall also reimburse the Investors for the
reasonable and documented fees and disbursements of Legal Counsel in connection
with registration, filing or qualification pursuant to Sections 2 and 3 of this
Agreement. The Company shall pay all of the Investors' reasonable costs
(including fees and disbursements of Legal Counsel) incurred in connection with
the successful enforcement of the Investors' rights under this Agreement.
Notwithstanding the foregoing, each seller of Registrable Securities shall pay
all fees and disbursements of all counsel (other than the Legal Counsel)
retained by such seller and all selling expenses, including, without limitation,
all underwriting discounts, selling commissions, transfer taxes and other
similar expenses, to the extent required by applicable law.

6.   INDEMNIFICATION.

     In the event any Registrable Securities are included in a Registration
Statement under this Agreement:

     (a) To the fullest extent permitted by law, the Company will, and hereby
does, indemnify, hold harmless and defend each Investor, the directors,
officers, partners, employees, agents, representatives of, and each Person, if
any, who controls any Investor within the meaning of the Securities Act or the
Exchange Act (each, an "INVESTOR INDEMNIFIED PERSON"), against any losses,
claims, damages, liabilities, judgments, fines, penalties, charges, costs,
reasonable attorneys' fees, amounts paid in settlement or expenses, joint or
several, (collectively, "CLAIMS") incurred in investigating, preparing or
defending any action, claim, suit, inquiry, proceeding, investigation or appeal
taken from the foregoing by or before any court or governmental, administrative
or other regulatory agency, body or the SEC, whether pending or threatened,
whether or not an indemnified party is or may be a party thereto ("INDEMNIFIED
DAMAGES"), to which any of them may become subject insofar as such Claims (or
actions or proceedings, whether commenced or threatened, in respect thereof)
arise out of or are based upon: (i) any untrue statement or alleged untrue
statement of a material fact in a Registration Statement or any post-effective
amendment thereto or in any filing made in connection with the qualification of
the offering under the securities or other "blue sky" laws of any jurisdiction
in which Registrable Securities are offered ("BLUE SKY FILING"), or the omission
or alleged omission to state a material


                                       12

fact required to be stated therein or necessary to make the statements therein
not misleading, (ii) any untrue statement or alleged untrue statement of a
material fact contained in any preliminary prospectus if used prior to the
effective date of such Registration Statement, or contained in the final
prospectus (as amended or supplemented, if the Company files any amendment
thereof or supplement thereto with the SEC) or the omission or alleged omission
to state therein any material fact necessary to make the statements made
therein, in light of the circumstances under which the statements therein were
made, not misleading, (iii) any violation or alleged violation by the Company of
the Securities Act, the Exchange Act, any other law, including, without
limitation, any state securities law, or any rule or regulation thereunder
relating to the offer or sale of the Registrable Securities pursuant to a
Registration Statement or (iv) any violation by the Company of the terms of this
Agreement (the matters in the foregoing clauses (i) through (iv) being,
collectively, "VIOLATIONS"). Subject to Section 6(c), the Company shall
reimburse the Investors and each such controlling person, promptly as such
expenses are incurred and are due and payable, for any legal fees or
disbursements or other reasonable expenses incurred by them in connection with
investigating or defending any such Claim. Notwithstanding anything to the
contrary contained herein, the indemnification agreement contained in this
Section 6(a): (i) shall not apply to a Claim by an Investor Indemnified Person
arising out of or based upon a Violation which occurs in reliance upon and in
conformity with information furnished in writing to the Company by such Investor
Indemnified Person expressly for use in connection with the preparation of the
Registration Statement or any such amendment thereof or supplement thereto, if
such prospectus was timely made available by the Company pursuant to Section
3(d); (ii) shall not be available to the extent such Claim is based on a failure
of the Investor to deliver or to cause to be delivered the prospectus made
available by the Company, (A) if such prospectus was timely made available by
the Company pursuant to Section 3(d) and (B) from and after December 1, 2005,
the Company had notified the Investor that such prospectus was required to be
delivered by the Investor as a result of the Company's failure to comply with
the conditions of Rule 172(c) under the Securities Act; and (iii) shall not
apply to amounts paid in settlement of any Claim, if such settlement is effected
without the prior written consent of the Company, which consent shall not be
unreasonably withheld. Such indemnity shall remain in full force and effect
regardless of any investigation made by or on behalf of the Investor Indemnified
Person and shall survive the transfer of the Registrable Securities by the
Investors pursuant to Section 9.

     (b) In connection with any Registration Statement in which an Investor is
participating, each such Investor agrees to severally and not jointly indemnify,
hold harmless and defend, to the same extent and in the same manner as is set
forth in Section 6(a), the Company, each of its directors, each of its officers
who signs the Registration Statement, each of the Company's agents or
representatives, and each Person, if any, who controls the Company within the
meaning of the Securities Act or the Exchange Act (each an "COMPANY INDEMNIFIED
PARTY"), against any Claim or Indemnified Damages to which any of them may
become subject, under the Securities Act, the Exchange Act or otherwise, insofar
as such Claim or Indemnified Damages arise out of or are based upon any
Violation, in each case to the extent, and only to the extent, that such
Violation occurs in reliance upon and in conformity with written information
furnished to the Company by such Investor specifically for use in connection
with such Registration Statement; and, subject to Section 6(d), such Investor
will reimburse any legal or other expenses reasonably incurred by them in
connection with investigating or defending any such Claim; provided, however,
that the indemnity agreement contained in this Section 6(b) and the agreement
with respect to contribution contained in Section 7 shall not apply to amounts
paid


                                       13

in settlement of any Claim if such settlement is effected without the prior
written consent of such Investor, which consent shall not be unreasonably
withheld; provided, further, however, that the Investor shall be liable under
this Section 6(b) for only that amount of a Claim or Indemnified Damages as does
not exceed the net proceeds to such Investor as a result of the sale of the
Registrable Securities pursuant to the Registration Statement giving rise to
such liability. Such indemnity shall remain in full force and effect regardless
of any investigation made by or on behalf of such Company Indemnified Party and
shall survive the transfer of the Registrable Securities by the Investors
pursuant to Section 9. Notwithstanding anything to the contrary contained
herein, the indemnification agreement contained in this Section 6(b) with
respect to any prospectus shall not inure to the benefit of any Company
Indemnified Party if the untrue statement or omission of material fact contained
in the prospectus was corrected on a timely basis in the prospectus, as then
amended or supplemented.

     (c) Promptly after receipt by an Investor Indemnified Person or Company
Indemnified Party under this Section 6 of notice of the commencement of any
action or proceeding (including any governmental action or proceeding) involving
a Claim, such Investor Indemnified Person or Company Indemnified Party shall, if
a Claim in respect thereof is to be made against any indemnifying party under
this Section 6, deliver to the indemnifying party a written notice of the
commencement thereof, and the indemnifying party shall have the right to
participate in, and, to the extent the indemnifying party so desires, jointly
with any other indemnifying party similarly noticed, to assume control of the
defense thereof with counsel mutually satisfactory to the indemnifying party and
the Investor Indemnified Person or the Company Indemnified Party, as the case
may be; provided, however, that an Investor Indemnified Person or Company
Indemnified Party shall have the right to retain its own counsel with the fees
and expenses of not more than one counsel for such Investor Indemnified Person
or Company Indemnified Party to be paid by the indemnifying party, if, in the
reasonable opinion of counsel retained by the indemnifying party, the
representation by such counsel of the Investor Indemnified Person or Company
Indemnified Party and the indemnifying party would be inappropriate due to
actual or potential conflicting interests between such Investor Indemnified
Person or Company Indemnified Party and any other party represented by such
counsel in such proceeding. In the case of an Investor Indemnified Person, legal
counsel referred to in the immediately preceding sentence (the "INVESTOR LEGAL
COUNSEL") shall be selected by the Investors holding a majority in interest of
the Registrable Securities included in the Registration Statement to which the
Claim relates. The Investor Legal Counsel shall not represent any Investor
Indemnified Person that sends such counsel written notice that such Investor
Indemnified Person does not wish such counsel to represent it in connection with
the matters discussed in this Section. The Investor Indemnified Persons, other
than any Investor Indemnified Person that delivers the notice discussed in the
preceding sentence, hereby waive any conflict of interest or potential conflict
of interest that may arise as a result of the representation of such Investor
Indemnified Persons by the Investor Legal Counsel in connection with the subject
matter of the Claim. The Company Indemnified Party or Investor Indemnified
Person shall cooperate with the indemnifying party in connection with any
negotiation or defense of any such action or claim by the indemnifying party and
shall furnish to the indemnifying party all information reasonably available to
the Company Indemnified Party or Investor Indemnified Person which relates to
such action or claim. The indemnifying party shall keep the Company Indemnified
Party or Investor Indemnified Person apprised as to the status of the defense or
any settlement negotiations with respect thereto. No indemnifying party shall be
liable for any


                                       14

settlement of any action, claim or proceeding effected without its prior written
consent, which consent shall not be unreasonably withheld. No indemnifying party
shall, without the prior written consent of the Company Indemnified Party or
Investor Indemnified Person, consent to entry of any judgment or enter into any
settlement or other compromise which (i) does not include as an unconditional
term thereof the giving by the claimant or plaintiff to such Company Indemnified
Party or Investor Indemnified Person of a release from all liability in respect
of such claim or litigation, (ii) requires any admission of wrongdoing by the
Company Indemnified Party or Investor Indemnified Party or (iii) obligates or
requires a Company Indemnified Party or Investor Indemnified Party to take, or
refrain from taking, any action. Following indemnification as provided for
hereunder, the indemnifying party shall be subrogated to all rights of the
Company Indemnified Party or Investor Indemnified Person with respect to all
third parties, firms or corporations relating to the matter for which
indemnification has been made. The failure to deliver written notice to the
indemnifying party within a reasonable time of the commencement of any such
action shall not relieve such indemnifying party of any liability to the
Investor Indemnified Person or Company Indemnified Party under this Section 6,
except to the extent that the indemnifying party is materially prejudiced in its
ability to defend such action.

     (d) The indemnification required by this Section 6 shall be made by
periodic payments of the amount thereof during the course of the investigation
or defense, as and when bills are received or Indemnified Damages are incurred.

     (e) The indemnity agreements contained herein shall be in addition to (i)
any cause of action or similar right of the Company Indemnified Party or
Investor Indemnified Person against the indemnifying party or others, and (ii)
any liabilities the indemnifying party may be subject to pursuant to the law.

7.   CONTRIBUTION.

     If for any reason the indemnification provided for in Section 6 hereof is
unavailable to a Company Indemnified Party or an Investor Indemnified Party or
insufficient to hold it harmless, other than as expressly specified therein,
then the indemnifying party shall contribute to the amount paid or payable by
the Company Indemnified Party or the Investor Indemnified Party, as applicable,
as a result of Claims in such proportion as is appropriate to reflect the
relative fault of the indemnified party and the indemnifying party, as well as
any other relevant equitable considerations. No person guilty of fraudulent
misrepresentation within the meaning of Section 11(f) of the Securities Act
shall be entitled to contribution from any person not guilty of such fraudulent
misrepresentation. In no event shall the contribution obligation of a holder of
Registrable Securities be greater in amount than the dollar amount of the
proceeds (net of all expenses paid by such holder in connection with any claim
relating to this Section 7 and the amount of any damages such holder has
otherwise been required to pay by reason of such untrue or alleged untrue
statement or omission or alleged omission) received by it upon the sale of the
Registrable Securities giving rise to such contribution obligation.

8.   REPORTS UNDER THE EXCHANGE ACT.

     With a view to making available to the Investors the benefits of Rule 144
promulgated under the Securities Act or any other similar rule or regulation of
the SEC that may at any time


                                       15

permit the Investors to sell securities of the Company to the public without
registration ("RULE 144"), the Company agrees to:

     (a) make and keep public information available, as those terms are
understood and defined in Rule 144;

     (b) file with the SEC in a timely manner all reports and other documents
required of the Company under the Securities Act and the Exchange Act so long as
the Company remains subject to such requirements (it being understood that
nothing herein shall limit the Company's obligations under the Securities
Purchase Agreement) and the filing of such reports and other documents is
required for the applicable provisions of Rule 144; and

     (c) furnish to each Investor so long as such Investor owns Registrable
Securities, promptly upon request, (i) a written statement by the Company that
it has complied with the reporting requirements of Rule 144, the Securities Act
and the Exchange Act and (ii) such other information as may be reasonably
requested to permit the investors to sell such securities pursuant to Rule 144
without registration.

9.   ASSIGNMENT OF REGISTRATION RIGHTS.

     The rights under this Agreement shall be automatically assignable by the
Investors to any transferee of all or any portion of Registrable Securities if:
(i) the Investor agrees in writing with the transferee or assignee to assign
such rights, and a copy of such agreement is furnished to the Company within a
reasonable time after such assignment; (ii) the Company is, within a reasonable
time after such transfer or assignment, furnished with written notice of (a) the
name and address of such transferee or assignee, and (b) the securities with
respect to which such registration rights are being transferred or assigned;
(iii) the transferee or assignee agrees in writing with the Company to be bound
by all of the provisions contained herein; and (iv) such transfer shall have
been made in accordance with the applicable requirements of the Securities
Purchase Agreement and Warrant. No transferee of registration rights under this
Agreement shall be entitled to include any Registrable Securities on a
Registration Statement unless it previously has provided the Company the written
notice referred to in clause (ii) of the preceding sentence.

10.  AMENDMENT OF REGISTRATION RIGHTS.

     Provisions of this Agreement may be amended and the observance thereof may
be waived (either generally or in a particular instance and either retroactively
or prospectively), only with the written consent of the Company and Investors
who then hold a majority of the Registrable Securities. Any amendment or waiver
effected in accordance with this Section 10 shall be binding upon each Investor
and the Company. No such amendment shall be effective to the extent that it
applies to less than all of the holders of the Registrable Securities.

11.  MISCELLANEOUS.

     (a) For the purposes of determining the rights of the Parties hereto,
including the right to approve matters pursuant to the terms hereof, a Person is
deemed to be a holder of Registrable Securities whenever such Person owns or is
deemed to own of record such Registrable Securities


                                       16

or holds Warrants exercisable for such Registrable Securities. When the number
of Registrable Securities shall be determined, the number shall be deemed to
include not only outstanding Common Shares but also any Common Shares issuable
pursuant to the terms of the Securities Purchase Agreement and Warrant Shares
issued upon the exercise of the Warrants. If the Company receives conflicting
instructions, notices or elections from two or more Persons with respect to the
same Registrable Securities, the Company shall act upon the basis of
instructions, notice or election received from the registered owner of such
Registrable Securities.

     (b) All notices, requests, consents, and other communications under this
Agreement shall be in writing and shall be deemed delivered (i) three business
days after being sent by registered or certified mail, return receipt requested,
postage prepaid, (ii) one business day after being sent via a reputable
nationwide overnight courier service guaranteeing next business day delivery or
(iii) upon delivery when sent by facsimile (with confirmation of receipt), in
each case to the intended recipient as set forth below:

          If to the Company:

          La Jolla Pharmaceutical Company
          6455 Nancy Ridge Drive
          San Diego, CA 92121
          Attention: Chief Executive Officer
          Fax: (858) 626-2851

or at such other address as may have been furnished in writing by the Company to
the other parties hereto, with a copy to:

          Gibson, Dunn & Crutcher LLP
          4 Park Plaza
          Irvine, CA 92614
          Attention: Mark W. Shurtleff
          Fax: (949) 451-4220

     If to a Purchaser, at its address set forth on the Schedule A, or at such
other address as may have been furnished in writing by such party to the
Company, with a copy to its legal counsel set forth on Schedule A, if any.

     If to Legal Counsel:

          Baker & McKenzie LLP
          130 East Randolph Drive
          Chicago, Illinois 60601
          Attention: Bruce Zivian, Esq.
          Fax: (312) 698-2469

     Any party may give any notice, request, consent or other communication
under this Agreement using any other means (including, without limitation,
personal delivery, messenger


                                       17

service or electronic mail), but no such notice, request, consent or other
communication shall be deemed to have been duly given unless and until it is
actually received by the party for whom it is intended. Any party may change the
address to which notices, requests, consents or other communications hereunder
are to be delivered by giving the other parties notice in the manner set forth
in this Section.

     (c) Failure of any party to exercise any right or remedy under this
Agreement or otherwise, or delay by a party in exercising such right or remedy,
shall not operate as a waiver thereof. If any provision of this Agreement shall
be invalid or unenforceable in any jurisdiction, such invalidity or
unenforceability shall not affect the validity or enforceability of the
remainder of this Agreement in that jurisdiction or the validity or
enforceability of any provision of this Agreement in any other jurisdiction.

     (d) This Agreement shall be governed by and construed in accordance with
the laws of the State of Delaware and the laws of the United States applicable
therein (in each case without giving effect to any choice or conflict of laws
provision or rule that would cause the application of the laws of any other
jurisdiction) and shall be treated in all respects as a Delaware contract. Any
action, suit or proceeding arising out of or relating to this Agreement shall be
brought in San Diego County, California or, if it has or can acquire
jurisdiction, any Federal court located in such State and County, and EACH OF
THE PARTIES HERETO, AFTER CONSULTING WITH OR HAVING HAD THE OPPORTUNITY TO
CONSULT WITH COUNSEL, HEREBY KNOWINGLY, VOLUNTARILY, INTENTIONALLY AND
IRREVOCABLY SUBMITS TO THE EXCLUSIVE JURISDICTION OF SUCH COURTS AND WAIVES
TRIAL BY JURY (AND AGREES NOT TO REQUEST TRIAL BY JURY), IN EACH CASE IN
CONNECTION WITH ANY ACTION, SUIT OR PROCEEDING ARISING OUT OF OR RELATING TO
THIS AGREEMENT. Each of the parties hereto hereby irrevocably and
unconditionally waives any objection to the laying of venue of any action, suit
or proceeding arising out of or relating to this Agreement or the transactions
contemplated hereby in the courts of the State of California or the United
States of America, in each case located in San Diego County, and hereby further
irrevocably and unconditionally waives and agrees not to plead or claim in any
such court that any such matter brought in any such court has been brought in an
inconvenient forum Each party hereby irrevocably waives personal service of
process and consents to process being served in any such suit, action or
proceeding by mailing a copy thereof to such party at the address for such
notices to it under this Agreement and agrees that such service shall constitute
good and sufficient service of process and notice thereof. Nothing contained
herein shall be deemed to limit in any way any right to serve process in any
manner permitted by law.

     (e) This Agreement, the Securities Purchase Agreement and the Warrants
constitute the entire agreement among the parties hereto with respect to the
subject matter hereof and thereof. There are no restrictions, promises,
warranties or undertakings, other than those set forth or referred to herein and
therein. This Agreement, the Securities Purchase Agreement and the Warrants
supersede all prior agreements and understandings among the parties hereto with
respect to the subject matter hereof and thereof.

     (f) Subject to the requirements of Section 9, this Agreement shall inure to
the benefit of and be binding upon the permitted successors and assigns of each
of the parties hereto.


                                       18

     (g) The headings in this Agreement are for convenience of reference only
and shall not limit or otherwise affect the meaning hereof.

     (h) This Agreement may be executed in identical counterparts, each of which
shall be deemed an original but all of which shall constitute one and the same
agreement. This Agreement, once executed by a party, may be delivered to the
other party hereto by facsimile transmission of a copy of this Agreement bearing
the signature of the party so delivering this Agreement.

     (i) Each party shall do and perform, or cause to be done and performed, all
such further acts and things, and shall execute and deliver all such other
agreements, certificates, instruments and documents, as the other party may
reasonably request in order to carry out the intent and accomplish the purposes
of this Agreement and the consummation of the transactions contemplated hereby.

     (j) All consents and other determinations to be made by the Investors
pursuant to this Agreement shall be made, unless otherwise specified in this
Agreement, by Investors holding a majority of the Registrable Securities,
determined as if all of the Common Shares issuable pursuant to the Purchase
Agreement had been issued and the Warrants then outstanding and exercisable have
been converted into or exercised for Registrable Securities without regard to
any limitation on the issuance of the Common Shares or exercise of the Warrants.

     (k) The language used in this Agreement will be deemed to be the language
chosen by the parties to express their mutual intent and no rules of strict
construction will be applied against any party.

     (l) This Agreement is intended for the benefit of the parties hereto and
their respective permitted successors and assigns, and is not for the benefit
of, nor may any provision hereof be enforced by, any other Person.


                                       19

     IN WITNESS WHEREOF, the parties have executed this Registration Rights
Agreement as of the date first set forth above.

THE COMPANY:                            LA JOLLA PHARMACEUTICAL COMPANY
                                        a Delaware corporation


                                        By: /s/ Steven B. Engle
                                            ------------------------------------
                                        Name: Steven B. Engle
                                              ----------------------------------
                                        Title: Chairman and CEO
                                               ---------------------------------


PURCHASERS:                             ESSEX WOODLANDS HEALTH VENTURES FUND VI,
                                        LP

                                        By: Essex Woodlands Health Ventures VI,
                                            L.P.
                                        Its: General Partner

                                        By: Essex Woodlands Health Ventures VI,
                                            L.L.C.
                                        Its: General Partner


                                        By: /s/ Martin P. Sutter
                                            ------------------------------------
                                            Martin P. Sutter, Managing Director


                                        DOMAIN PUBLIC EQUITY PARTNERS, L.P.

                                        By:  Domain Public Equity Associates,
                                        L.L.C., its General Partner

                                        By: /s/ Lisa A. Kraeutler
                                            ------------------------------------
                                            Lisa A. Kraeutler, Attorney-in-Fact


                                        /s/ Alejandro Gonzalez Cimadevilla
                                        ----------------------------------------
                                        Alejandro Gonzalez Cimadevilla


                                        SPECIAL SITUATIONS FUND III, L.P.

                                        By: /s/ Austin W. Marxe
                                            ------------------------------------
                                            Austin W. Marxe, its General Partner





                                  SPECIAL SITUATIONS CAYMAN FUND, L.P.


                                  By: /s/ Austin W. Marxe
                                      ------------------------------------------
                                      Austin W. Marxe, its General Partner


                                  SPECIAL SITUATIONS PRIVATE EQUITY FUND, L.P.

                                  By: /s/ Austin W. Marxe
                                      ------------------------------------------
                                      Austin W. Marxe, its General Partner


                                  SPECIAL SITUATIONS LIFE SCIENCES FUND, L.P.

                                  By: /s/ Austin W. Marxe
                                      ------------------------------------------
                                      Austin W. Marxe, its General Partner


                                  SUTTER HILL VENTURES,
                                  a California limited partnership

                                  By: /s/ William H. Younger, Jr.
                                      ------------------------------------------
                                      William H. Younger Jr.
                                      Managing Director of the General
                                      Partner



                                  ANVEST, L.P.

                                  By: /s/ David Anderson
                                      ------------------------------------------
                                      David Anderson, General Partner


                                  G. LEONARD BAKER, JR. AND MARY ANNE BAKER,
                                  CO-TRUSTEES OF THE BAKER REVOCABLE TRUST
                                  U/A/D 2/3/03

                                  By: /s/ G. Leonard Baker, Jr.
                                      By David E. Sweet Under Power of Attorney
                                      ------------------------------------------
                                      G. Leonard Baker, Jr., Trustee


                                  WILLIAM H. YOUNGER, JR. AND LAUREN L.
                                  YOUNGER, CO-TRUSTEES OF THE YOUNGER LIVING
                                  TRUST U/A/D 1/20/95

                                  By: /s/ William H. Younger, Jr.
                                      ------------------------------------------
                                      William H. Younger, Jr., Trustee


                                  TENCH COXE AND SIMONE OTUS COXE,
                                  CO-TRUSTEES OF THE COXE REVOCABLE TRUST
                                  U/A/D 4/23/98

                                  By: /s/ Tench Coxe By David E. Sweet
                                      Under Power of Attorney
                                      ------------------------------------------
                                      Tench Coxe, Trustee

                                  /s/ James C. Gaither By David E. Sweet
                                  Under Power of Attorney
                                  ----------------------------------------------
                                  James C. Gaither


                                  JEFFREY W. BIRD AND CHRISTINA R. BIRD AS
                                  TRUSTEES OF JEFFREY W. AND CHRISTINA R.
                                  BIRD TRUST AGREEMENT DATED 10/31/00

                                  By: /s/ Jeffrey W. Bird
                                      ------------------------------------------
                                      Jeffrey W. Bird, Trustee


                                  SAUNDERS HOLDINGS, L.P.

                                  By: /s/ G. Leonard Baker, Jr.
                                      By David E. Sweet Under Power of Attorney
                                      ------------------------------------------
                                      G. Leonard Baker, Jr., General Partner



                                  ROBERT YIN AND LILY YIN AS TRUSTEES OF YIN
                                  FAMILY TRUST DATED MARCH 1, 1997

                                  By: /s/ Robert Yin
                                      ------------------------------------------
                                      Robert Yin, Trustee


                                  WELLS FARGO BANK, N.A. FBO
                                  SHV PROFIT SHARING PLAN FBO SHERRYL W.
                                  HOSSACK


                                  /s/ Vicki M. Bandel
                                  ----------------------------------------------

                                  WELLS FARGO BANK, N.A. FBO
                                  SHV PROFIT SHARING PLAN FBO DAVID L.
                                  ANDERSON


                                  /s/ Vicki M. Bandel
                                  ----------------------------------------------


                                  WELLS FARGO BANK, N.A. FBO
                                  SHV PROFIT SHARING PLAN FBO WILLIAM H.
                                  YOUNGER

                                  /s/ Vicki M. Bandel
                                  ----------------------------------------------


                                  WELLS FARGO BANK, N.A. FBO
                                  SHV PROFIT SHARING PLAN FBO TENCHE COXE

                                  /s/ Vicki M. Bandel
                                  ----------------------------------------------


                                  WELLS FARGO BANK, N.A. FBO
                                  SHV PROFIT SHARING PLAN FBO DAVID E. SWEET

                                  /s/ Vicki M. Bandel
                                  ----------------------------------------------


                                  WELLS FARGO BANK, N.A. FBO
                                  SHV PROFIT SHARING PLAN FBO DAVID E. SWEET
                                  (ROLLOVER)

                                  /s/ Vicki M. Bandel
                                  ----------------------------------------------


                                  WELLS FARGO BANK, N.A. FBO
                                  SHV PROFIT SHARING PLAN FBO LYNNE M. BROWN

                                  /s/ Vicki M. Bandel
                                  ----------------------------------------------


                                  WELLS FARGO BANK, N.A. FBO
                                  SHV PROFIT SHARING PLAN FBO PATRICIA TOM
                                  (POST)

                                  /s/ Vicki M. Bandel
                                  ----------------------------------------------

                             SCHEDULE OF PURCHASERS



                                                    INVESTOR ADDRESS          INVESTOR'S REPRESENTATIVES' ADDRESS
               INVESTOR NAME                      AND FACSIMILE NUMBER                AND FACSIMILE NUMBER
               -------------                      --------------------        -----------------------------------
                                                                        
Essex Woodlands Health Ventures Fund VI,     10001 Woodloch Forest Drive      Baker & McKenzie LLP
L.P.                                         Waterway Plaza Two, Suite 175    130 E. Randolph Drive
                                             The Woodlands, TX 77380          Chicago, IL 60601
                                             Attn: Martin P. Sutter           Attn: Bruce Zivian, Esq.
                                             Fax: (281) 364-9755              Fax: (312) 698-2469

Frazier Healthcare V, LP                     601 Union Street,
                                             Suite 3200
                                             Seattle, WA 98101
                                             Attn: James Topper
                                             Fax: (206) 621-1848

Alejandro Gonzalez Cimadevilla               Ruben Dario #223 5-A
                                             Chapultepec Morales
                                             Mexico D.F. ZIP 11570
                                             Fax: (5255) 52818008

Domain Public Equity Partners, L.P.          One Palmer Square, Suite 515
                                             Princeton, NJ 08542
                                             Attn: Nicole Vitullo
                                             Fax: (609) 683-4581

Special Situations Fund III, L.P.            153 E. 53rd Street, 55th Floor   Lowenstein Sandler PC
                                             New York, NY 10022               65 Livingston Avenue
                                             Attn: Marianne Hicks             Roseland, NJ 07068
                                             Fax: 212-207-6515                Attn: John D. Hogoboom, Esq.
                                                                              Fax: (973) 597-2383

Special Situations Cayman Fund, L.P.         153 E. 53rd Street, 55th Floor   Lowenstein Sandler PC
                                             New York, NY 10022               65 Livingston Avenue
                                             Attn: Marianne Hicks             Roseland, NJ 07068
                                             Fax: 212-207-6515                Attn: John D. Hogoboom, Esq.
                                                                              Fax: (973) 597-2383

Special Situations Private Equity Fund,      153 E. 53rd Street, 55th Floor   Lowenstein Sandler PC
L.P.                                         New York, NY 10022               65 Livingston Avenue
                                             Attn: Marianne Hicks             Roseland, NJ 07068
                                             Fax: 212-207-6515                Attn: John D. Hogoboom, Esq.
                                                                              Fax: (973) 597-2383

Special Situations Life Sciences Fund,       153 E. 53rd Street, 55th Floor   Lowenstein Sandler PC
L.P.                                         New York, NY 10022               65 Livingston Avenue
                                             Attn: Marianne Hicks             Roseland, NJ 07068
                                             Fax: 212-207-6515                Attn: John D. Hogoboom, Esq.
                                                                              Fax: (973) 597-2383

Sutter Hill Ventures                         755 Page Mill Road
                                             Suite A-200
                                             Palo Alto, CA 94304
                                             Attn: Robert Yin
                                             Fax: 650-493-5600






                                                    INVESTOR ADDRESS          INVESTOR'S REPRESENTATIVES' ADDRESS
               INVESTOR NAME                      AND FACSIMILE NUMBER                AND FACSIMILE NUMBER
               -------------                      --------------------        -----------------------------------
                                                                        
Anvest, L.P.                                 c/o Sutter Hill Ventures
                                             755 Page Mill Road
                                             Suite A-200
                                             Palo Alto, CA 94304
                                             Attn: Robert Yin
                                             Fax (650) 493-5600

G. Leonard Baker, Jr. and Mary Anne Baker,   c/o Sutter Hill Ventures
Co-Trustees of The Baker Revocable Trust     755 Page Mill Road
U/A/D 2/3/03                                 Suite A-200
                                             Palo Alto, CA 94304
                                             Attn: Robert Yin
                                             Fax (650) 493-5600

Saunders Holdings, L.P.                      c/o Sutter Hill Ventures
                                             755 Page Mill Road
                                             Suite A-200
                                             Palo Alto, CA 94304
                                             Attn: Robert Yin
                                             Fax (650) 493-5600

William H. Younger, Jr. and                  c/o Sutter Hill Ventures
Lauren L. Younger, Co-Trustees of The        755 Page Mill Road
Younger Living Trust U/A/D 1/20/95           Suite A-200
                                             Palo Alto, CA 94304
                                             Attn: Robert Yin
                                             Fax (650) 493-5600

Tench Coxe and Simone Otus Coxe,             c/o Sutter Hill Ventures
Co-Trustees of The Coxe Revocable Trust      755 Page Mill Road
U/A/D 4/23/98                                Suite A-200
                                             Palo Alto, CA 94304
                                             Attn: Robert Yin
                                             Fax (650) 493-5600

James C. Gaither                             c/o Sutter Hill Ventures
                                             755 Page Mill Road
                                             Suite A-200
                                             Palo Alto, CA 94304
                                             Attn: Robert Yin
                                             Fax (650) 493-5600

Jeffrey W. Bird and Christina R. Bird as     c/o Sutter Hill Ventures
Trustees of Jeffrey W. and Christina R.      755 Page Mill Road
Bird Trust Agreement Dated 10/31/00          Suite A-200
                                             Palo Alto, CA 94304
                                             Attn: Robert Yin
                                             Fax (650) 493-5600

Robert Yin and Lily Yin as Trustees of       c/o Sutter Hill Ventures
Yin Family Trust Dated March 1, 1997         755 Page Mill Road
                                             Suite A-200
                                             Palo Alto, CA 94304
                                             Attn: Robert Yin
                                             Fax (650) 493-5600

Wells Fargo Bank, N.A. FBO                   Attention: Vicki Bandel
SHV Profit Sharing Plan FBO Sherryl W.       420 Montgomery Street, 2nd Fl.
Hossack                                      San Francisco, CA 94101
                                             Fax: 415-956-9362

Wells Fargo Bank, N.A. FBO                   Attention: Vicki Bandel
SHV Profit Sharing Plan FBO David L.         420 Montgomery Street, 2nd Fl.
Anderson                                     San Francisco, CA 94101
                                             Fax: 415-956-9362






                                                    INVESTOR ADDRESS          INVESTOR'S REPRESENTATIVES' ADDRESS
               INVESTOR NAME                      AND FACSIMILE NUMBER                AND FACSIMILE NUMBER
               -------------                      --------------------        -----------------------------------
                                                                        
Wells Fargo Bank, N.A. FBO                   Attention: Vicki Bandel
SHV Profit Sharing Plan FBO William H.       420 Montgomery Street, 2nd Fl.
Younger, Jr.                                 San Francisco, CA 94101
                                             Fax: 415-956-9362

Wells Fargo Bank, N.A. FBO                   Attention: Vicki Bandel
SHV Profit Sharing Plan FBO Tench Coxe       420 Montgomery Street, 2nd Fl.
                                             San Francisco, CA 94101
                                             Fax: 415-956-9362

Wells Fargo Bank, N.A. FBO SHV Profit        Attention: Vicki Bandel
Sharing Plan FBO David E. Sweet              420 Montgomery Street, 2nd Fl.
                                             San Francisco, CA 94101
                                             Fax: 415-956-9362

Wells Fargo Bank, N.A. FBO SHV Profit        Attention: Vicki Bandel
Sharing Plan FBO David E. Sweet (Rollover)   420 Montgomery Street, 2nd Fl.
                                             San Francisco, CA 94101
                                             Fax: 415-956-9362

Wells Fargo Bank, N.A. FBO SHV Profit        Attention: Vicki Bandel
Sharing Plan FBO Lynne M. Brown              420 Montgomery Street, 2nd Fl.
                                             San Francisco, CA 94101
                                             Fax: 415-956-9362

Wells Fargo Bank, N.A. FBO SHV Profit        Attention: Vicki Bandel
Sharing Plan FBO Patricia Tom (Post)         420 Montgomery Street, 2nd Fl.
                                             San Francisco, CA 94101
                                             Fax: 415-956-9362