Celgene Corporation

                         Registration Rights Agreement

         THIS REGISTRATION RIGHTS AGREEMENT (the 'Agreement') is entered into as
of July ___, 1995, by and among Celgene Corporation, a Delaware corporation (the
'Company'),  and the persons and  entities  listed on Exhibit A attached  hereto
(the 'Investors').

                                   Recitals:

WHEREAS,  pursuant to a Regulation S Subscription  Agreement (the  'Subscription
Agreement'),  by and among the Company and the Investors, the Company has agreed
to sell  and the  Investors  have  agreed  to  purchase  up to an  aggregate  of
$12,000,000 U.S.  principal  amount 8% Convertible  Debentures due July 31, 1997
(the  'Debentures')  of the Company  convertible  into  shares of the  Company's
Common Stock, par value $.01 per share (the 'Shares');

WHEREAS,  pursuant  to the terms  of,  and in  partial  consideration  for,  the
Investors' agreement to enter into the Subscription  Agreement,  the Company has
agreed to provide the Investors with certain registration rights with respect to
the Shares;

NOW  THEREFORE,  in  consideration  of  the  mutual  promises,  representations,
warranties, covenants and conditions set forth in the Subscription Agreement and
this  Registration  Rights  Agreement,  the Company and the  Investors  agree as
follows:

                                   Agreement:

         1.  Certain Definitions. As used in this Agreement, the following terms
             shall have the following respective meanings:

         'Commission'  shall mean the Securities and Exchange  Commission or any
other Federal agency at the time administering the Securities Act.

         'Common  Stock' shall mean the Company's  Common Stock,  par value $.01
per share.

         'Initiating  Holders'  shall  mean  holders  of  Debentures  having  an
aggregate principal amount of $3 million or more.

         'Other Registrable  Securities' shall mean those shares of Common Stock
heretofore or hereafter  issued pursuant to one or more agreements  granting the
purchasers  of such  securities  the  right to have the  Company  register  such
securities or include such securities in any other registration of the Company's
equity securities.

         'Registrable  Shares'  shall  mean (i) the  Shares,  (ii)  the  Warrant
Shares,  and (iii) any Common Stock of the Company issued or issuable in respect
of the Shares or the Warrant  Shares or upon any stock  split,  stock  dividend,
recapitalization  or similar  event;  provided,  however,  that shares of Common
Stock or other  securities  shall no longer be treated as Registrable  Shares if
(A) they  have been sold to or  through a broker or dealer or  underwriter  in a
public distribution or a public securities transaction,  (B) they have been sold
in  a  transaction   exempt  from  the  registration  and  prospectus   delivery
requirements  of the  Securities  Act so  that  all  transfer  restrictions  and
restrictive  legends with respect thereto are




removed upon  consummation of such sale or (C) the Shares are available for sale
under Rule 144, in the  opinion of counsel to the  Company,  without  compliance
with the registration and prospectus delivery requirements of the Securities Act
so that all transfer  restrictions and restrictive  legends with respect thereto
may be removed upon the consummation of such sale.

         The terms 'register',  'registered' and 'registration' shall refer to a
registration  effected  by  preparing  and filing a  registration  statement  in
compliance  with  the  Securities  Act  and  applicable  rules  and  regulations
thereunder,  and  the  declaration  or  ordering  of the  effectiveness  of such
registration statement.

         'Registration  Expenses' shall mean all expense incurred by the Company
in  compliance  with  Section  2  hereof,  including,  without  limitation,  all
registration  and filing fees,  printing  expenses,  fees and  disbursements  of
counsel  for the  Company,  blue  sky  fees and  expenses,  reasonable  fees and
disbursements (not to exceed $10,000) of one counsel for all the selling holders
of Registrable Shares for a limited 'due diligence'  examination of the Company,
and the reasonable expenses of any special audits incident to or required by any
such  registration  (but excluding the compensation of regular  employees of the
Company, which shall be paid in any event by the Company).

         'Securities Act' shall mean the Securities Act of 1933, as amended,  or
any similar  federal  statute,  and the rules and  regulations of the Commission
thereunder, all as the same shall be in effect at the time.

         'Selling  Expenses' shall mean all  underwriting  discounts and selling
commissions  applicable  to the  sale of  Registrable  Shares  and all  fees and
disbursements  of one  counsel  for the selling  holders of  Registrable  Shares
(other than the fees  disbursements  of such  counsel  included in  Registration
Expenses).

         'Warrant  Shares'  shall mean the shares of Common  Stock  issuable  on
exercise of Warrant(s)  issued to Swartz  Investments,  Inc., in connection with
the issuance of the Debentures.

         2.  Requested Registration.

         The following  registration rights will apply only if at any time prior
the  expiration of these rights,  Regulation S promulgated  under the Securities
Act is rescinded or modified so as to preclude  non-United  States  persons from
reselling in United States public  securities  markets shares  received from the
Company,  or if, for any other reason, the Company refuses to issue unrestricted
Shares to an Investor  after the Restricted  Period,  as that term is defined in
the Debentures:

                  (a) Request for  Registration.  If the Company  shall  receive
from Initiating  Holders,  at any time after four (4) months following the final
closing of the sale of Debentures  pursuant to the  Subscription  Agreements,  a
written request that the Company effect a registration  with respect to all, but
not less than all, of the  Registrable  Shares held by such  Initiating  Holders
(which notice shall  specify the intended  method of  disposition),  the Company
shall:

                           (i)  promptly give written notice of the proposed 
registration to all other holders of Registrable Shares; and

                           (ii) as soon as  practicable  use its best efforts to
effect such registration  (including,  without  limitation,  the execution of an
undertaking to file post-




effective  amendments,  appropriate  qualification  under applicable blue sky or
other  state   securities  laws  and  appropriate   compliance  with  applicable
regulations issued under the Securities Act) as may be so requested and as would
permit or facilitate  the sale and  distribution  of all or such portion of such
Registrable  Shares as are specified in such request,  together with all or such
portion of the Registrable Shares of any holder or holders of Registrable Shares
joining in such request as are  specified in a written  request  given within 15
days after  receipt of such written  notice from the Company;  provided that the
Company shall not be obligated to effect,  or to take any action to effect,  any
such registration pursuant to this Section 2:

                                    (A) after the Company has  effected one such
                           registration  pursuant to this Section 2 (a) and such
                           registration  has been declared or ordered  effective
                           by the  Commission  and the sale of such  Registrable
                           Shares shall have closed; or

                                    (B) within the period starting with the date
                           60 days prior to the Company's  good faith  estimated
                           date of filing of, and ending 180 days  following the
                           effective  date of, any  registered  offering  of the
                           Company's securities to the general public.

                            Subject to the foregoing  limitations in clauses (A)
and (B) above,  the Company  shall file a  registration  statement  covering the
Registrable  Shares so requested to be registered as soon as  practicable  after
receipt of the request or requests of the Initiating Holders,  but no later than
45 days following receipt of such request or requests;  provided,  however, that
if the Company shall furnish to such holders of Registrable Shares a certificate
signed by the President of the Company  stating that in the good faith  judgment
of the Board of Directors it would be seriously  detrimental  to the Company and
its stockholders for such registration  statement to be filed within such 45 day
period and it is therefore  advisable  to defer the filing of such  registration
statement, the Company shall have an additional period of up to 45 days (and not
to exceed the period  reasonably  determined  by the  Company to be  necessary),
after the  expiration  of such initial  45-day  period within which to file such
registration  of such initial 45-day period,  provided that during such time the
Company may not file a  registration  statement for  securities to be issued and
sold for its own account.

         The  registration  statement  filed  pursuant  to  the  request  of the
Initiating Holders may, subject to the provision of Section 2(b) below,  include
Other Registrable Securities,  other securities of the Company which are held by
officers  or  directors  of the  Company  or which are held by other  holders of
registration  rights,  and may include  securities of the Company being sold for
the account of the Company.

         (b)  Underwriting.  If the Initiating  Holders intend to distribute the
Registrable  Shares covered by their request by means of an  underwriting,  they
shall so advise the Company as a part of their  request made pursuant to Section
2 and the Company shall include such  information in the written notice referred
to in Section 2 (a) (i) above. The right of any holder of Registrable  Shares to
registration  pursuant  to  Section 2 shall be  conditioned  upon such  holder's
participation   in  such   underwriting  and  the  inclusion  of  such  holder's
Registrable Shares in such underwriting  (unless other wise mutually agreed by a
majority in interest of the  Initiating  Holders and such holder with respect to
such  participation  and inclusion) to the extent provided  herein.  A holder of
Registrable  Shares may elect to include in such  underwriting  all or a part of
the Registrable Shares it holds.

                  (i) If the Company shall request inclusion in any registration
pursuant  to  Section 2 of  securities  being  sold for its own  account,  or if
officers or directors of the





Company holding other securities of the Company or other holders of registration
rights,  shall request inclusion in any registration  pursuant to Section 2, the
Initiating Holders shall, on behalf of all holders of Registrable Shares,  offer
to include Other Registrable  Securities and the securities of the Company, such
officers and  directors  and such other  holders of  registration  rights in the
underwriting  and may  condition  such offer on their  acceptance of the further
applicable  provisions of this  Agreement.  The Company shall (together with all
holders  of  Registrable  Shares,  officers  and  directors,  other  holders  of
registration  rights and holders of Other  Registrable  Securities  proposing to
distribute  their   securities   through  such   underwriting)   enter  into  an
underwriting  agreement in customary form with the underwriter or representative
of the  underwriters  selected  for  such  underwriting  by the  Company,  which
underwriter(s)  shall be reasonably  acceptable to a majority in interest of the
Initiating Holders.

                  (ii) Notwithstanding any other provision of this Section 2, if
the  representative  of the  underwriters  advises the  Company in writing  that
marketing   factors  require  a  limitation  on  the  number  of  shares  to  be
underwritten,  the Company shall so advise all holders of Registrable Shares and
other  shareholders  whose securities  would otherwise be underwritten  pursuant
hereto,  and the number of Registrable  Shares and other  securities that may be
included  in  the  registration  and  underwriting  shall  be  allocated  in the
following  manner:  the securities of the Company held by officers and directors
of the  Company  (other than  Registrable  Shares)  shall be excluded  from such
registration and underwriting to the extent required by such limitation, and, if
a limitation on the number of shares is still  required,  the Other  Registrable
Securities  shall be excluded pro rata with Registrable  Shares,  unless another
method of determining  such  exclusion is specified in the agreements  governing
the Other  Registrable  Securities,  according to the  relative  number of Other
Registrable  Securities  requested  to be  included  in  such  registration  and
underwriting,  from such registration and underwriting to the extent required by
such limitation, and, if a limitation on the number of shares is still required,
the number of Registrable  Shares that may be included in the  registration  and
underwriting  shall be  allocated  among all  holders of  Registrable  Shares in
proportion,  as nearly as practicable,  to the respective amounts of Registrable
Shares which they had requested to be included in such  registration at the time
of  filing  the  registration  statement.  No  Registrable  Shares  or any other
securities  excluded  from  the  underwriting  by  reason  of the  underwriter's
marketing limitation shall also be included in such registration.

                  (iii) If the  Company or any  officer,  director  or holder of
Registrable Shares or Other Registrable  Securities who has requested  inclusion
in such registration and underwriting as provided above disapproves of the terms
of the  underwriting,  such  person may elect to withdraw  therefrom  by written
notice  to  the  Company,  the  underwriter  and  the  Initiating  Holders.  The
securities so withdrawn shall also be withdrawn from registration.

         3. Expenses of  Registration.  The Company shall bear all  Registration
Expenses  incurred  in  connection  with  any  registration,   qualification  or
compliance of the Registrable  Shares  pursuant to this  Agreement.  All Selling
Expenses  shall be borne by the holder of the  securities so registered pro rata
on the basis of the number of their shares so registered.

                            4.   Registration   Procedures.   Pursuant  to  this
Agreement,  the Company will keep each holder of  Registrable  Shares advised in
writing as to the  initiation of a  registration  under this Agreement and as to
the completion thereof. At its expense, the Company will:
                  (a) Use reasonable efforts to keep such registration effective
for a period of 180 days or until the holder or holders  of  Registrable  Shares
have completed the distribution described in the registration statement relating
thereto, whichever first occurs;




                  (b) Prepare and file with the Commission  such  amendments and
supplements to such registration statement and the prospectus used in connection
with  such  registration  statement  as may be  necessary  to  comply  with  the
provisions of the Securities  Act with respect to the  disposition of securities
covered by such registration statement; and

                  (c) Furnish such number of  prospectuses  and other  documents
incidental thereto,  including any amendment of or supplement to the prospectus,
as a holder of Registrable Securities from time to time may reasonably request.

         5.  Indemnification.

                  (a) The Company  will  indemnify  each  holder of  Registrable
Shares,  each  of  its  officers,   directors  and  partners,  and  each  person
controlling   such  holder  of  Registrable   Shares,   with  respect  to  which
registration has been effected pursuant to this Agreement, and each underwriter,
if any and each  person  who  controls  any  underwriter,  and their  respective
counsel  against  all  claims,  losses,  damages and  liabilities  (or  actions,
proceedings or settlements  in respect  thereof)  arising out of or based on any
untrue  statement (or alleged untrue  statement) of a material fact contained in
any prospectus, or other document incident to any such registration, or based on
any omission (or alleged  omission) to state therein a material fact required to
be stated therein or necessary to make the statements therein not misleading, or
any  violation by the Company of the  Securities  Act or any rule or  regulation
thereunder  applicable to the Company in connection  with any such  registration
and will reimburse each such holder of Registrable Shares, each of its officers,
directors and partners,  and each person  controlling such holder of Registrable
Shares, each such underwriter and each person who controls any such underwriter,
for any  legal  and any  other  expenses  as they  are  reasonably  incurred  in
connection  with  investigating  and  defending  any such claim,  loss,  damage,
liability or action,  provided,  however,  that the indemnity  contained in this
Section  5(a) shall not apply to amounts paid in  settlement  of any such claim,
loss,  damage,  liability or action if such  Settlement is effected  without the
consent of the  Company;  and  provided  further  that the Company  shall not be
liable  in any  such  case to the  extent  that any such  claim,  loss,  damage,
liability  or  expense  arises  out of or is based on any  untrue  statement  or
omission based upon written information  furnished to the Company by such holder
of  Registrable  Shares or  underwriter  and stated to be  specifically  for use
therein.  The foregoing  indemnity agreement is further subject to the condition
that insofar as it relates to any untrue  statement,  alleged untrue  statement,
omission or alleged  omission made in a preliminary  prospectus,  such indemnity
agreement shall not inure to the benefit of the foregoing indemnified parties if
copies  of  a  final  prospectus   correcting  the   misstatement,   or  alleged
misstatement,  omission  or alleged  omission  upon which such loss,  liability,
claim or damage is based is timely  delivered  to such  indemnified  party and a
copy thereof was not  furnished  to the person  asserting  the loss,  liability,
claim or damage.

         (b) Each holder of Registrable  Shares will, if Registrable Shares held
by it are  included in the  securities  as to which such  registration  is being
effected,  indemnify  the Company,  each of its  directors and officers and each
underwriter,  if any, of the Company's securities covered by such a registration
statement,  each person who controls the Company or such underwriter  within the
meaning of the Securities  Act and the rules and  regulations  thereunder,  each
other such holder of Registrable Shares and each of its officers,  directors and
partners,  and each person  controlling such holder of Registrable  Shares,  and
their respective counsel against all claims, losses, damages and liabilities (or
actions,  proceedings or settlements in respect thereof) arising out of or based
on any untrue  statement  (or  alleged  untrue  statement)  of a  material  fact
relating  to  such  Holder  contained  in  any  such   registration   statement,
prospectus,  offering  circular or other  document,  or any omission (or alleged
omission)  to state  therein a  material  fact  required  to be  stated  therein
relating to such holder or necessary




to make the  statements  therein  relating to such holder not  misleading or any
violation  by such  holder  of any  rule or  regulation  promulgated  under  the
Securities  Act  applicable  to such  holder and  relating to action or inaction
required  of such  holder in  connection  with any such  registration;  and will
reimburse the Company, such holders of Registrable Shares, directors,  officers,
partners,  persons,  underwriters  or control persons for any legal or any other
expense  reasonably  incurred in connection with  investigating or defending any
such claim, loss, damage,  liability or action , in each case to the extent, but
only to the extent,  that such untrue statement (or alleged untrue statement) or
omission  (or  alleged  omission)  relating  to  such  holder  is  made  in such
registration  statement,  prospectus,  offering  circular  or other  document in
reliance  upon and in  conformity  with  written  information  furnished  to the
Company by such holder of Registrable  Shares and stated to be specifically  for
use  therein;  provided,  however,  that  the  obligations  of such  holders  of
Registrable Shares hereunder shall be limited to an amount equal to the proceeds
to each such  holder  of  Registrable  Shares  of  securities  sold  under  such
registration  statement,  prospectus,  offering  circular  or other  document as
contemplated herein and provided further that such  indemnification  obligations
shall not apply if the Company  modifies or changes to a material extent written
information furnished by such Holder.

         (c) Each party  entitled to  indemnification  under this Section 5 (the
'Indemnified  Party')  shall  give  notice  to the  party  required  to  provide
indemnification (the 'Indemnifying Party') promptly after such Indemnified Party
has actual knowledge of any claim as to which indemnity may be sought, and shall
permit the  Indemnifying  Party to assume  the  defense of any such claim or any
litigation  resulting  therefrom,  provided  that  counsel for the  Indemnifying
Party,  who shall conduct the defense of such claim or any litigation  resulting
therefrom, shall be approved by the Indemnified Party, (whose approval shall not
unreasonably be withheld or delayed),  and the Indemnified Party may participate
in such defense at such indemnified  party's expense,  and provided further that
the failure of any Indemnified Party to give notice as provided herein shall not
relieve the  Indemnifying  Party of its  obligations  under this  Agreement.  No
Indemnifying Party, in the defense of any such claim or litigation, shall except
with the consent of each Indemnified Party,  consent to entry of any judgment or
enter into any  settlement  which  does not  include  as an  unconditional  term
thereof the giving by the claimant or plaintiff to such  Indemnified  Party of a
release  from  all  liability  in  respect  to such  claim or  litigation.  Each
Indemnified  Party shall furnish such information  regarding itself or the claim
in question as an  Indemnifying  Party may reasonably  request in writing and as
shall be  reasonably  required  in  connection  with  defense  of such claim and
litigation resulting therefrom.

         6.  Information  by  Holder  of  Registrable  Shares.  Each  holder  of
Registrable Shares shall furnish to the Company such information  regarding such
holder of  Registrable  Shares and the  distribution  proposed by such holder of
Registrable Shares as the Company may reasonably request in writing and as shall
be reasonably  required in connection with any registration  referred to in this
Agreement.

         7. No transfer or Assignment of  Registration  Rights.  Each Investor's
rights under this  Agreement  to cause the Company to register  the  Registrable
Shares may be transferred  or assigned by an Investor  (other than to affiliates
of such Investors) only to a purchaser of a Debenture in the principal amount of
at least $1,000,000 or at least 125,000 shares and such assignment shall only be
effective  upon  delivery of written  notice of such  assignment  to the Company
within thirty (30) days of the assignment.






         8.  Miscellaneous.

            8.1  Governing  Law.   This  agreement  shall  be  governed  by  and
construed in accordance  with the laws of the State of Delaware  without  giving
effect to conflict of laws.
            8.2 Successors and Assigns. Except as otherwise provided herein, the
provisions  hereof  shall  inure to the  benefit  of, and be binding  upon,  the
successors, assigns, heirs, executors and administrators of the parties hereto.

            8.3 Entire Agreement. This Agreement constitutes the full and entire
understanding  and  agreement  between  the  parties  with regard to the subject
matter hereof.
            8.4 Notices,  etc. All notices and other communications  required or
permitted hereunder shall be in writing and shall be mailed by first-class mail,
postage  prepaid,  or  delivered  by hand or by  messenger  or courier  delivery
service,  addressed (a) if to an Investor,  at such Investor's address set forth
on  Exhibit A hereof,  or at such  other  address  as such  Investor  shall have
furnished to the Company in writing,  or (b) if to the  Company,  at the address
set forth on the  signature  page hereof or at such other address as the Company
shall have furnished to each Investor and each such other holder in writing.

            8.5 Delays or Omissions. No delay or omission to exercise any right,
power or remedy  accruing  to any  holder of any  Registrable  Shares,  upon any
breach or default of the Company  under this  Agreement,  shall  impair any such
right,  power or remedy of such holder nor shall it be  construed to be a waiver
of any such  breach or  default,  or an  acquiescence  therein,  or of or in any
similar  breach or  default  thereunder  occurring;  nor shall any waiver of any
single  breach or  default  be deemed a waiver  of any other  breach or  default
thereafter  occurring.  Any waiver,  permit,  consent or approval of any kind or
character  on the  part of any  holder  of any  breach  or  default  under  this
Agreement,  or any  waiver  on  the  part  of any  party  of any  provisions  or
conditions of this Agreement,  must be in writing and shall be effective only to
the extent  specifically set forth in such writing.  All remedies,  either under
this  Agreement,  or by law  or  otherwise  afforded  to any  holder,  shall  be
cumulative and not alternative.

            8.6  Counterparts.  This  agreement may be executed in any number of
counterparts,  each of which may be executed by less than all of the  Investors,
each of which shall be enforceable  against the parties actually  executing such
counterparts, and all of which together shall constitute one instrument.

            8.7. Severability. In the case any provision of this agreement shall
be invalid, illegal or unenforceable,  the validity, legality and enforceability
of the  remaining  provisions  shall  not in any  way be  affected  or  impaired
thereby.
            8.8  Amendments.  The provisions of this Agreement may be amended at
any time and from time to time, and particular  provisions of this Agreement may
be waived,  with and only with an agreement or consent in writing  signed by the
Company and by the Investors  currently holding 50% of the Registrable Shares as
of the date of such amendment or waiver.

            8.9  Termination  of  Registration   Rights.  This  Agreement  shall
terminate  at the earlier of July 28, 1997 and at such time as there cease to be
any outstanding shares which constitutes Registrable Shares as defined herein.

The foregoing  Registration  Rights  Agreement is hereby executed as of the date
first above written.




Celgene Corporation                                           Investors


By:  ___________________________            _________________________________

Title:  __________________________          By:  ____________________________

Address: 7 Powder Horn Drive                Name:  __________________________
              Warren, NJ 07059
              Attn: Mr. Richard G. Wright   Title: ___________________________
              Fax: (908)805-3931