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                                                                     Exhibit 2.3
                                                         AS EXECUTED - CONFORMED

                    KBLP ASSIGNMENT AND ASSUMPTION AGREEMENT


            ASSIGNMENT AND ASSUMPTION AGREEMENT, dated as of July 1, 1998,
between KB USA, L.P., a Delaware limited partnership ("KBLP"), and ASTRA
PHARMACEUTICALS, L.P., a Delaware limited partnership (the "Partnership").

                                   WITNESSETH:

            WHEREAS, Astra AB, a company limited by shares organized and
existing under the laws of Sweden ("KB"), Merck & Co., Inc., a New Jersey
corporation ("TR"), Astra Merck Inc., a Delaware corporation ("KBI"), KBLP, the
Partnership and other related parties have entered into that certain Master
Restructuring Agreement dated as of June 19, 1998 (the "Master Restructuring
Agreement");

            WHEREAS, KB, TR, KB USA and KBLP have executed and delivered the KB
USA Asset Contribution Agreement dated as of June 19, 1998 (the "KB USA Asset
Contribution Agreement") providing for the transfer and assignment of certain
assets of KB USA to KBLP and the assumption by KBLP of certain liabilities and
obligations of KB USA;

            WHEREAS, KBLP desires to transfer and assign all of its rights and
obligations under the KB USA Asset Contribution Agreement to the Partnership,
and the Partnership desires to accept and assume such rights and obligations,
all in accordance with the terms and conditions of this Agreement and the Master
Restructuring Agreement;

            NOW, THEREFORE, in consideration of the premises and the agreements
contained herein and in the Master Restructuring Agreement, the parties hereby
agree as follows:

            1. Definitions. Capitalized terms that are used herein and not
otherwise defined shall have the respective meanings assigned to them in the KB
USA Asset Contribution Agreement.

            2. Assignment. Effective at and as of the Effective Time (as defined
in the Master Restructuring Agreement), KBLP hereby conveys, grants, transfers,
sets over, assigns and delivers to the Partnership all of KBLP's rights in and
under the KB USA Asset Contribution Agreement.

            3. Assumption. Effective at and as of the Effective Time, the
Partnership, without any further responsibility or liability of, or recourse to,
KB USA, KBLP or any of their respective directors, shareholders, officers,
employees, agents, consultants, representatives, Affiliates, successors or
assigns hereby absolutely and irrevocably assumes and is, and shall be, liable
and solely responsible for any and all liabilities and obligations of KBLP under
or pursuant to the KB USA Asset Contribution Agreement, including without
limitation all Assumed Liabilities (as defined in the KB USA Asset Contribution
Agreement).
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            4. Performance of Obligations by the Partnership; Indemnification.
(a) The Partnership covenants and agrees to perform and satisfy fully, on or
before the date when due, all obligations included in, arising from, or related
to, the Assumed Liabilities so that KB USA, KBLP and all of their respective
directors, shareholders, officers, employees, agents, consultants,
representatives, Affiliates, successors or assigns have no liability or
obligations with respect thereto.

            (b) The Partnership agrees to indemnify, defend and hold harmless
KBLP and its Affiliates and their respective officers, directors, employees and
agents from and against any and all Indemnity Losses (as defined in the Master
Restructuring Agreement) arising out of, based upon or resulting from (i) the
liabilities and obligations of KBLP under the KB USA Asset Contribution
Agreement and (ii) the Assumed Liabilities. Any claim for indemnification
hereunder shall be on a net-after tax basis in accordance with, and shall be
subject to the procedures set forth in, Section 10.3 of the Master Restructuring
Agreement.

            5. Certain Related Provisions. This Agreement is subject to Articles
9, 10 and 12 of the Master Restructuring Agreement.
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            IN WITNESS WHEREOF, the parties have caused this Agreement to be
duly executed as of the date first above written.

                                          KB USA, L.P.

                                          By:  ASTRA AB, General Partner
                                                 (publ)



                                          By:   /s/ Goran Lerenius
                                             -----------------------------------
                                             Name:    Goran Lerenius
                                             Title:   Authorized Signatory




                                          ASTRA PHARMACEUTICALS, L.P.

                                          By:   KB USA, L.P., General Partner

                                          By:  ASTRA AB, General Partner
                                                 (publ)



                                          By:   /s/ Goran Lerenius
                                             -----------------------------------
                                             Name:    Goran Lerenius
                                             Title:   Authorized Signatory