STOCK OPTION AGREEMENT (this "Agreement"), dated as of September 21,
 1999, between MedImmune, Inc., a Delaware corporation ("Grantee"), and U.S.
 Bioscience, Inc., a Delaware corporation ("Issuer").

                                  RECITALS

      A.  Grantee, Marlin Merger Sub Inc., a wholly owned subsidiary of
 Grantee ("Sub"), and Issuer have entered into an Agreement and Plan of
 Merger, dated as of the date hereof (the "Merger Agreement"; defined terms
 used but not defined herein have the meanings set forth in the Merger
 Agreement), providing for, among other things, the merger of Sub with and
 into Issuer; and

      B.  As a condition and inducement to Grantee's willingness to enter
 into the Merger Agreement, Grantee has requested that Issuer agree, and
 Issuer has agreed, to grant Grantee the Option (as defined below).

      NOW, THEREFORE, in consideration of the foregoing and the respective
 representations, warranties, covenants and agreements set forth herein,
 Issuer and Grantee agree as follows:

      1.   Grant of Option.  Subject to the terms and conditions set forth
 herein, Issuer hereby grants to Grantee an irrevocable option (the
 "Option") to purchase that number of shares which equals 19.9% of the
 issued and outstanding Issuer Common Shares (the "Option Shares")
 immediately prior to the exercise of this Option at a price per share (the
 "Option Price") equal to $16.50, payable in cash.  The number of Option
 Shares and the Option Price are subject to adjustment as set forth herein.

      2.   Exercise and Termination of Option.  (a)  If Grantee is not in
 material breach of the Merger Agreement, subject to the terms and
 conditions hereof, Grantee may exercise the Option in whole at any time
 after the occurrence of a Trigger Event and prior to the close of business
 on the Termination Date (the "Exercisability Period").  "Trigger Event"
 shall mean an event which obligates Issuer to pay the Termination Fee
 pursuant to Section 5.8(b) of the Merger Agreement. "Termination Date"
 shall mean the earliest of (i) the Effective Time of the Merger, (ii) 180
 days after the date full payment contemplated by Section 5.8(b) of the
 Merger Agreement is made by Issuer to Grantee thereunder, (iii) the
 termination of the Merger Agreement so long as no Trigger Event has
 occurred or could still occur pursuant to Section 5.8(b) the Merger
 Agreement or (iv) 13 months after the termination of the Merger Agreement
 under circumstances which could result in Grantee's becoming entitled to
 receive the Termination Fee from Issuer pursuant to Section 5.8(b), unless
 during such 13 month period a Trigger Event shall occur. Notwithstanding
 the occurrence of the Termination Date, Grantee shall be entitled to
 purchase the Option Shares pursuant to the exercise of the Stock Option, on
 the terms and subject to the conditions hereof, to the extent Grantee
 exercised the Stock Option prior to the occurrence of the Termination Date.

           (b)  If Grantee is entitled to and wishes to exercise the Option,
 it shall deliver to Issuer a written notice (the date of receipt of which
 is referred to as the "Notice Date") specifying (i) it intends to such
 exercise and (ii) a place and date not earlier than three business days nor
 later than 15 business days from the Notice Date for the closing of such
 purchase; provided that if the closing of the purchase and sale pursuant to
 the Option (the "Closing") cannot be consummated by reason of any
 applicable judgment, decree, order, law or regulation, the period of time
 that otherwise would run pursuant to this sentence shall run instead from
 the date on which such restriction on consummation has expired or been
 terminated; and, provided further that, without limiting the foregoing, if
 prior notification to or approval of any regulatory authority is required
 in connection with such purchase, Grantee and, if applicable, Issuer shall
 promptly file the required notice or application for approval and shall
 expeditiously process the same (and Issuer shall cooperate with Grantee in
 the filing of any such notice or application and the obtaining of any such
 approval), and the period of time that otherwise would run pursuant to this
 sentence shall run instead from the date on which, as the case may be, (i)
 any required notification period has expired or been terminated or (ii)
 such approval has been obtained, and in either event, any requisite waiting
 period has passed.  Issuer shall take any action reasonably requested by
 Grantee to cause the Closing to occur as promptly as practicable. Any
 exercise of the Option shall be deemed to occur on the Notice Date relating
 thereto.  Any extensions of the periods specified in this Section 2(b)
 shall extend the Exercisability Period on a day for day basis.

           (c)  Notwithstanding anything herein to the contrary, it shall be
 a condition to the exercise of this Option and the purchase of the Option
 Shares that (i) no preliminary or permanent injunction or other order,
 decree or ruling against the sale or delivery of the Option Shares issued
 by any federal or state court of competent jurisdiction in the United
 States is in effect at such time, (ii) any applicable waiting period under
 the Hart-Scott-Rodino Antitrust Improvements Act of 1976 (the "HSR Act")
 shall have expired or been terminated at or prior to such time, and (iii)
 any approval required to be obtained prior to the delivery of the Option
 Shares under the laws of any jurisdiction shall have been obtained and
 shall be in full force and effect.

      3.   Payment and Delivery of Certificates.

           (a)  At the Option Closing, Grantee will pay to Issuer in
 immediately available funds by wire transfer to a bank account designated
 in writing by Issuer an amount equal to the Purchase Price multiplied by
 the number of Option Shares to be purchased at such Option Closing;
 provided that failure or refusal of Issuer to designate such a bank account
 shall not preclude Grantee from exercising the Option.

           (b)  At the Option Closing, simultaneously with the delivery of
 immediately available funds as provided in Section 3(a), Issuer will
 deliver, or cause to be delivered, to Grantee a certificate or certificates
 representing the Option Shares to be purchased at such Option Closing,
 which Option Shares will be fully paid and non-assessable and free and
 clear of all Liens (except for any such Lien due to the issuance of the
 Option Shares not being registered under the Securities Act and Liens
 arising from acts of Grantee). If at the time of issuance of Option Shares
 pursuant to an exercise of the Option hereunder, Issuer shall have issued
 any securities similar to rights under a shareholder rights plan, then each
 Option Share issued pursuant to such exercise will also represent such a
 corresponding right with terms substantially the same as and at least as
 favorable to Grantee as are provided under any such shareholder rights plan
 then in effect.

           (c)  Certificates for the Option Shares delivered at the Option
 Closing will have typed or printed thereon a restrictive legend which will
 read substantially as follows:

      "THE SECURITIES REPRESENTED BY THIS CERTIFICATE HAVE NOT BEEN
      REGISTERED UNDER THE SECURITIES ACT OF 1933 AND MAY BE REOFFERED OR
      SOLD ONLY IF SO REGISTERED OR IF AN EXEMPTION FROM SUCH REGISTRATION
      IS AVAILABLE."

      It is understood and agreed that such legend will be removed by
 delivery of substitute certificate(s) without such reference if such Option
 Shares have been registered pursuant to the Securities Act, or Grantee has
 delivered to Issuer a copy of a letter from the staff of the SEC, or an
 opinion of counsel in customary form to the effect that such legend is not
 required for purposes of the Securities Act.

           (d)  Subject to applicable laws, when the Grantee provides the
 Exercise Notice and the tender of the applicable purchase price in
 immediately available funds (or offer of such tender if the proviso to the
 Section 3(a) is applicable), the Grantee shall be deemed to be the holder
 of record of the Issuer Common Shares issuable upon such exercise,
 notwithstanding that the stock transfer books of Issuer shall then be
 closed or that certificates representing such Issuer Common Shares shall
 not then be actually delivered to the Grantee.

      4.   Representations and Warranties of Issuer. Issuer hereby
 represents and warrants to Grantee as follows:

           (a)  Issuer is a corporation duly organized, validly existing and
 in good standing under the laws of the State of Delaware.  The execution,
 delivery and performance by Issuer of this Agreement and the consummation
 of the transactions contemplated hereby (i) are within Issuer's corporate
 powers, (ii) have been duly authorized by all necessary corporate action,
 (iii)  require no action by or in respect of, or filing with, any
 Governmental Entity, except for compliance with any applicable requirements
 of the HSR Act and any applicable filings and approvals under similar
 foreign antitrust laws and regulations and such filings with and approvals
 of the American Stock Exchange necessary to permit the Options Shares to be
 traded on the American Stock Exchange, (iv) do not contravene, or conflict
 with the certificate of incorporation or by-laws of Issuer, (v) do not
 contravene or conflict with or constitute a violation of any provision of
 any law, regulation or judgment, injunction, order or decree binding upon
 Issuer or any of its subsidiaries and (vi) will not require any consent,
 approval or notice under and will not conflict with, or result in the
 breach or termination of any provision of or constitute a default (with or
 without the giving of notice or the lapse of time or both) under, or allow
 the acceleration of the performance of, any material obligation of Issuer
 or any of its Subsidiaries under, or result in the creation of a Lien upon,
 any of the properties, assets or business of Issuer or any of its
 Subsidiaries under any indenture, mortgage, deed of trust, lease, licensing
 agreement, contract, instrument or other agreement to which Issuer or any
 of its Subsidiaries is a party or by which Issuer or any of its
 Subsidiaries or any of their respective assets or properties is subject or
 bound other than, in the case of each of (iii), (iv), (v) or (vi), any such
 items that would not, individually or in the aggregate, be reasonably
 likely to have a Material Adverse Effect on Issuer or prevent or materially
 impair the ability of Issuer to consummate the transactions contemplated by
 this Agreement.  This Agreement has been duly executed and delivered by
 Issuer and constitutes a valid and binding agreement of Issuer, enforceable
 in accordance with its terms (except insofar as enforceability may be
 limited by applicable bankruptcy, insolvency, reorganization, moratiorium
 or other similar laws affecting creditors' rights generally or by
 principles governing availability of equitable remedies).

           (b)  Except for any filings required to be made under the HSR Act
 and any applicable filings and approvals under similar foreign antitrust
 laws and regulations and such filings with and approvals of the American
 Stock Exchange necessary to permit the Options Shares to be traded on the
 American Stock Exchange, Issuer has taken all necessary corporate and other
 action to authorize and reserve and to permit it to issue, and at all times
 from the date hereof until such time as the obligation to deliver Option
 Shares upon the exercise of the Option terminates, will have reserved for
 issuance, upon any exercise of the Option, the number of Option Shares
 subject to the Option.  All of the Issuer Common Shares to be issued
 pursuant to the Option are duly authorized and, upon issuance and delivery
 thereof pursuant to this Agreement, will be duly authorized, validly
 issued, fully paid and nonassessable, and free and clear of all Liens
 (except for any such Lien due to the issuance of the Option Shares not
 being registered under the Securities Act and Liens arising from acts of
 Grantee), and not subject to any preemptive rights.

      5.   Representations and Warranties of Grantee. Grantee hereby
 represents and warrants to Issuer that:

           (a)  Grantee is a corporation duly organized, validly existing
 and in good standing under the laws of the State of Delaware.  The
 execution, delivery and performance by Grantee of this Agreement and the
 consummation of the transactions contemplated hereby (i)  are within
 Grantee's corporate powers, (ii)  have been duly authorized by all
 necessary corporate action.

           (b)  The Option Shares or other securities acquired by Grantee
 upon exercise of the Option will not be and the option is not being
 acquired by Grantee with the intention of making a public distribution
 thereof and the Option Shares will not be transferred or otherwise disposed
 of except in a transaction registered, or exempt from registration, under
 the Securities Act.

      6.   Adjustment upon Changes in Capitalization, Etc.

           (a)  In the event of any change in Issuer Common Shares by reason
 of stock dividends, stock splits, split-ups, spin-offs, recapitalizations,
 recombinations, extraordinary dividends or the like, the type and number of
 Option Shares, and the Option Price, as the case may be, shall be adjusted
 appropriately to reflect such event and proper provision shall be made in
 any agreement governing any such transaction to provide for such adjustment
 and the full satisfaction of the Issuer's obligations hereunder, provided
 that in no event shall the number of shares of Issuer Common Stock subject
 to the Option exceed 19.9% of the number of shares of Issuer Common Stock
 issued and outstanding on the date of exercise.

           (b)  Without limiting the parties' relative rights and
 obligations under the Merger Agreement, if the Issuer enters into an
 agreement with respect to an Takeover Proposal or other transaction
 involving the exchange or conversion of Issuer Common Shares for shares or
 other securities of the Issuer or another person, then the agreement
 governing such transaction shall make proper provision so that the Option
 shall, upon the consummation of any such transaction and upon the terms and
 conditions set forth herein, be converted into, or exchanged for, an option
 with identical terms appropriately adjusted to acquire the number and class
 of shares or other securities or property that Grantee would have received
 in respect of Issuer Common Shares if the Option had been exercised
 immediately prior to the consummation of such Takeover Proposal, or the
 record date therefor, as applicable.

           (c)  If, at any time during the Exercisability Period, Grantee
 sends to Issuer a notice (a "Cash-Out Notice") indicating Grantee's
 election to exercise its right pursuant to this Section 6(c), then Issuer
 shall pay to Grantee, on the date specified in the Cash-Out Notice, which
 shall be a date not earlier than three business days nor later than 15
 business days from the Cash-Out Notice, in exchange for the cancellation of
 the Option (if the Option has not been exercised) or the repurchase of any
 Issuer Common Shares issued to Grantee pursuant hereto which Grantee then
 beneficially owns and has requested that Issuer repurchase (if the Option
 has been exercised), at a price per share equal to the higher of (x) if
 applicable, the highest price per share of Common Stock paid or proposed to
 be paid by any Person pursuant to any Takeover Proposal (non-cash
 consideration to be valued as set forth in Section 7(e) hereof) or (y) the
 average of the closing prices of the shares of Common Stock on the
 principal securities exchange or quotation system on which the Common Stock
 is then listed or traded as reported in The Wall Street Journal (or another
 authoritative source) for the five consecutive trading days immediately
 preceding the date of the Cash-Out Notice, less, if the Option has not been
 exercised, the Option Price in respect of each Option Share being
 cancelled. Notwithstanding the termination of the Option, Grantee will be
 entitled to exercise its rights under this Section 6(c) if it has exercised
 such rights in accordance with the terms hereof prior to the termination of
 the Option.  The payment contemplated by this Section 6(c) shall be made in
 immediately available funds to an account specified by Grantee.  Amounts
 paid under this Section shall be suject to Section 7(a) hereof.

      7.   Profit Limitations.

           (a)  Notwithstanding any other provision of this Agreement, in no
 event shall the Total Option Profit (as hereinafter defined) exceed in the
 aggregate $17 million minus the sum of any Termination Fee plus Expenses
 actually received by Grantee pursuant to the terms of the Merger Agreement
 (such amount, the "Profit Limit") and, if any payment to be made to Grantee
 otherwise would cause such aggregate amount to be exceeded, the Grantee, at
 its sole election, shall either (i) reduce the number of Issuer Common
 Shares subject to this Option, (ii) pay cash to Issuer, (iii) waive rights
 under this Agreement or (iv) any combination thereof, so that the Total
 Option Profit shall not exceed the Profit Limit after taking into account
 the foregoing actions.

           (b)  Notwithstanding any other provision of this Agreement, this
 Option may not be exercised for a number of Issuer Common Shares as would,
 as of the date of exercise, result in a Notional Total Option Profit (as
 hereinafter defined) which would exceed in the aggregate the Profit Limit
 and, if it otherwise would exceed such amount, the Grantee, at its sole
 election, shall on or prior to the date of exercise either (i) reduce the
 number of Issuer Common Shares subject to such exercise, (ii) pay cash to
 Issuer, (iii) waive rights under this Agreement or (iv) any combination
 thereof, so that the Notional Total Option Profit shall not exceed the
 Profit Limit after taking into account the foregoing actions, provided that
 this paragraph (b) shall not be construed as to restrict any exercise of
 the Option in whole that is not prohibited hereby on any subsequent date.

           (c)  As used herein, the term "Total Option Profit" shall mean
 the aggregate amount (before taxes) of the following: (i) any amount
 received by Grantee pursuant to the Cash-Out Right and (ii)(x) the net
 consideration, if any, received by Grantee pursuant to the sale of Option
 Shares (or any other securities into which such Option Shares are converted
 or exchanged) to any unaffiliated party, valuing any non-cash consideration
 at its fair market value (as defined below), less (y) the Exercise Price
 and any cash paid by Grantee to Issuer pursuant to Section 7(a)(iii) or
 Section 7(b)(iii), as the case may be.

           (d)  As used herein, the term "Notional Total Option Profit" with
 respect to the number of Issuer Common Shares as to which Grantee may
 propose to exercise the Option shall be the Total Option Profit with
 respect to such number of Issuer Common Shares as to which Grantee proposes
 to exercise and all other Option Shares held by Grantee and its affiliates
 as of such date, assuming that all such shares were sold for cash at the
 closing market price for Issuer Common Shares as of the close of business
 on the preceding trading day (less customary brokerage commissions or
 underwriting discounts).

           (e)  As used herein, the "fair market value" of any non-cash
 consideration consisting of:

                (i)  securities listed on a national securities exchange or
 traded on NASDAQ shall be equal to the average closing price per share of
 such security as reported on such exchange or NASDAQ for the five trading
 days before the date of determination; and

                (ii) consideration which is other than cash or securities of
 the form specified in clause (i) above shall be determined by a nationally
 recognized independent investment banking firm mutually agreed upon by the
 parties five business days prior to the event requiring selection of such
 banking firm, provided that if the parties are unable to agree within three
 business days as to the investment banking firm, then the parties shall
 each select one firm, and those firms shall select a third nationally
 recognized independent investment banking firm 48 hours, which third firm
 shall make such determination as promptly as reasonably practicable.  The
 third firm's determination shall be final and binding on each of the
 parties.

      8.   Registration Rights. Issuer will, if requested by Grantee at any
 time and from time to time within three years of the exercise of the
 Option, as promptly as practicable (but in no event later than 90 days
 after receipt of such request) prepare and file up to three registration
 statements under the Securities Act if such registration is necessary in
 order to permit the sale or other disposition of any or all shares of
 securities that have been acquired by or are issuable to Grantee upon
 exercise of the Option in accordance with the intended method of sale or
 other disposition stated by Grantee, including a "shelf" registration
 statement under Rule 415 under the Securities Act or any successor
 provision, and Issuer will use its best efforts to qualify such shares or
 other securities under any applicable state securities laws. A Registration
 Statement shall not be deemed filed if it is withdrawn by Issuer, subject
 to a stop or similar order or not kept effective in accordance with the
 following sentence. Issuer will use reasonable efforts to cause each such
 registration statement to become effective, to obtain all consents or
 waivers of other parties which are required therefor, and to keep such
 registration statement effective for such period not in excess of 180
 calendar days from the day such registration statement first becomes
 effective as may be reasonably necessary to effect such sale or other
 disposition. The obligations of Issuer hereunder to file a registration
 statement and to maintain its effectiveness may be suspended for up to 60
 calendar days in the aggregate if the Board of Directors of Issuer shall
 have determined that the filing of such registration statement or the
 maintenance of its effectiveness would require premature disclosure of
 material nonpublic information that would materially and adversely affect
 Issuer or otherwise interfere with or adversely affect any pending or
 proposed offering of securities of Issuer or any other material transaction
 involving Issuer. Any registration statement prepared and filed under this
 Section 8, and any sale covered thereby, will be at Issuer's expense except
 for underwriting discounts or commissions, brokers' fees and the fees and
 disbursements of Grantee's counsel related thereto. Grantee will provide
 all information reasonably requested by Issuer for inclusion in any
 registration statement to be filed hereunder. If, during the time periods
 referred to in the first sentence of this Section 8, Issuer effects a
 registration under the Securities Act of Issuer Common Shares for its own
 account or for any other stockholders of Issuer (other than on Form S-4 or
 Form S-8, or any successor form), it will allow Grantee the right to
 participate in such registration, and such participation will not affect
 the obligation of Issuer to effect demand registration statements for
 Grantee under this Section 8; provided that, if the managing underwriters
 of such offering advise Issuer in writing that in their opinion the number
 of Issuer Common Shares requested to be included in such registration
 exceeds the number which can be sold in such offering, Issuer will include
 only the shares requested to be included therein by Grantee that may be
 included therein without adversely affecting the success of the offering.
 In connection with any registration pursuant to this Section 8, Issuer and
 Grantee will provide each other and any underwriter of the offering with
 customary representations, warranties, covenants, indemnification, and
 contribution in connection with such registration.

      9.   Listing. If Issuer Common Shares or any other securities to be
 acquired upon exercise of the Option are then listed on The Nasdaq National
 Market (or any other national securities exchange or national securities
 quotation system), Issuer, upon the request of Grantee, will promptly file
 an application to list the Issuer Common Shares or other securities to be
 acquired upon exercise of the Option on The Nasdaq National Market (or any
 such other national securities exchange or national securities quotation
 system) and will use reasonable efforts to obtain approval of such listing
 as promptly as practicable.

      10.  Loss or Mutilation. Upon receipt by Issuer of evidence reasonably
 satisfactory to it of the loss, theft, destruction or mutilation of this
 Agreement, and (in the case of loss, theft or destruction) of reasonably
 satisfactory indemnification, and upon surrender and cancellation of this
 Agreement, if mutilated, Issuer will execute and deliver a new Agreement of
 like tenor and date.

      11.  Miscellaneous.

           (a)  Expenses. Except as otherwise provided in this Agreement or
 in the Merger Agreement, each of the parties hereto will bear and pay all
 costs and expenses incurred by it or on its behalf in connection with the
 transactions contemplated hereunder, including fees and expenses of its own
 financial consultants, investment bankers, accountants, and counsel.

           (b)  Amendment. This Agreement may not be amended, except by an
 instrument in writing signed on behalf of each of the parties.

           (c)  Extension; Waiver. Any agreement on the part of a party to
 waive any provision of this Agreement, or to extend the time for
 performance, will be valid only if set forth in an instrument in writing
 signed on behalf of such party. The failure of any party to this Agreement
 to assert any of its rights under this Agreement or otherwise will not
 constitute a waiver of such rights.

           (d)  Entire Agreement; Third-Party Beneficiaries. This Agreement,
 the Merger Agreement (including the documents and instruments attached
 thereto as exhibits or schedules or delivered in connection therewith) and
 the Confidentiality Agreement (i) constitute the entire agreement, and
 supersede all prior agreements and understandings, both written and oral,
 between the parties with respect to the subject matter of this Agreement,
 and (ii) except as provided in Section 8.06 of the Merger Agreement, are
 not intended to confer upon any Person other than the parties any rights or
 remedies.

           (e)  Governing Law. This Agreement will be governed by, and
 construed in accordance with, the laws of the State of Delaware, regardless
 of the laws that might otherwise govern under applicable principles of
 conflict of laws thereof.

           (f)  Notices. All notices, requests, claims, demands, and other
 communications under this Agreement shall be sent in the manner and to the
 addresses set forth in the Merger Agreement.

           (g)  Assignment. Neither this Agreement, the Option nor any of
 the rights, interests, or obligations under this Agreement may be assigned
 or delegated, in whole or in part, by operation of law or otherwise, by
 Issuer or Grantee without the prior written consent of the other, except
 that Grantee may assign, in its sole discretion, any of or all its rights,
 interests and obligations under this Agreement to any direct or indirect
 wholly owned Subsidiary of Grantee, but no such assignment shall relieve
 Grantee of any of its obligations hereunder. Any assignment or delegation
 in violation of the preceding sentence will be void. Subject to the first
 and second sentences of this Section 11(g), this Agreement will be binding
 upon, inure to the benefit of, and be enforceable by, the parties and their
 respective successors and assigns.

           (h)  Further Assurances. In the event of any exercise of the
 Option by Grantee, Issuer and Grantee will execute and deliver all other
 documents and instruments and take all other actions that may be reasonably
 necessary in order to consummate the transactions provided for by such
 exercise.  Issuer will not take any actions which would frustrate the
 exercise of the Option or the other transactions contemplated hereby.

           (i)  Section 16(b).  Any time period hereunder shall be extended
 to the extent necessary for any Grantee to avoid liability under Section
 16(b) of the Exchange Act.

           (j)  Enforcement. The parties agree that irreparable damage would
 occur and that the parties would not have any adequate remedy at law in the
 event that any of the provisions of this Agreement were not performed in
 accordance with their specific terms or were otherwise breached. It is
 accordingly agreed that the parties will be entitled to an injunction or
 injunctions to prevent breaches of this Agreement and to enforce
 specifically the terms and provisions of this Agreement in any Federal
 court located in the State of Delaware or in any state court located in the
 State of Delaware, the foregoing being in addition to any other remedy to
 which they are entitled at law or in equity. In addition, each of the
 parties hereto (i) consents to submit itself to the personal jurisdiction
 of any Federal court located in the State of Delaware or any state court
 located in the State of Delaware in the event any dispute arises out of
 this Agreement or any of the transactions contemplated by this Agreement,
 (ii) agrees that it will not attempt to deny or defeat such personal
 jurisdiction by motion or other request for leave from any such court, and
 (iii) agrees that it will not bring any action relating to this Agreement
 or any of the transactions contemplated by this Agreement in any court
 other than a Federal court sitting in the State of Delaware or a state
 court located in the State of Delaware.

           (k)  Severability. If any term or other provision of this
 Agreement is invalid, illegal or incapable of being enforced by any rule of
 law or public policy, all other conditions and provisions of this Agreement
 shall nevertheless remain in full force and effect. Upon such determination
 that any term or other provision is invalid, illegal or incapable of being
 enforced, the parties hereto shall negotiate in good faith to modify this
 Agreement so as to effect the original intent of the parties as closely as
 possible to the fullest extent permitted by applicable law in an acceptable
 manner to the end that the transactions contemplated hereby are fulfilled
 to the extent possible.

      IN WITNESS WHEREOF, Issuer and Grantee have caused this Agreement to
 be signed by their respective officers thereunto duly authorized as of the
 day and year first written above.


                               MEDIMMUNE, INC.

                               /s/ Wayne T. Hockmeyer
                               --------------------------------------------
                               Name:  Wayne T. Hockmeyer
                               Title: Chairman and Chief Executive Officer


                               U.S. BIOSCIENCES, INC.

                               /s/ C. Boyd Clarke
                               --------------------------------------------
                               Name:  C. Boyd Clarke
                               Title: President and Chief Executive Officer