1
CONTRACT A                                                         EXHIBIT 10.73

                                  CONFIRMATION

Date:               September 11, 1997

To:                 IDEC Pharmaceuticals Corporation ("Party B")

Attention:          Phillip Schneider

From:               Swiss Bank Corporation, London Branch ("Party A")

Re:                 Equity Option Confirmation 
                    Reference Number 1262211/ 1262212
- --------------------------------------------------------------------------------
The purpose of this communication is to confirm the terms and conditions of the
transaction (the "Transaction") entered into between us on the Trade Date
specified below.

The definitions and provisions contained in the 1991 ISDA Definitions (as
published by the International Swaps and Derivatives Association, Inc. (formerly
known as the International Swap Dealers Association, Inc.) ("ISDA")) are
incorporated into this Confirmation. In the event of any inconsistency between
those definitions and provisions and this Confirmation, this Confirmation will
govern.

This Confirmation supplements, forms part of, and is subject to, the ISDA Master
Agreement dated as of August 26, 1997, as amended and supplemented from time to
time (the "Agreement"), between you and Swiss Bank Corporation. All provisions
contained in the Agreement govern this Confirmation except as expressly modified
below.

The terms of the Transaction to which this Confirmation relates are as follows:

Trade Date            :      *________* 

Buyer                 :      Party B

Seller                :      Party A

Option Style          :      European Option

- ----------

 *________* Indicates that material has been omitted and confidential
treatment has been requested therefor. All such omitted material has been filed
separately with Secretary of the Commission in the Company's Application
Requesting Confidential Treatment pursuant to Rule 24b-2 under the Securities
Exchange Act of 1934, as amended.

   2


Option Type                  :      Capped Call

Shares                       :      Common Stock of IDEC Pharmaceuticals 
                                    Corporation (Symbol: IDPH)

Number of Options            :      600,000

Contract Multiplier          :      1.00

Strike Price                 :      *________*

Cap Price                    :      USD 46.40

Total Premium                :      *________*.

Expiration Date              :      *________*, or, if that date is not an 
                                     Exchange Business Day, the following day
                                     that is an Exchange Business Day.

Currency
Business Day                 :       Any day on which commercial banks are open
                                     for business (including dealings in foreign
                                     exchange and foreign currency deposits) in
                                     the cities from which and in which a
                                     payment is to be made.

Exchange
Business Day                 :       A day that is (or but for the occurrence of
                                     a Market Disruption Event, would have been)
                                     a trading day on the Exchange and the
                                     Pacific Stock Exchange (other than a day on
                                     which trading on any such exchange is
                                     scheduled to close prior to its regular
                                     weekday closing time, first announced on
                                     the day of such closing).

Normal
Trading Day                  :       An Exchange Business Day on which no Market
                                     Disruption Event has occurred or is
                                     continuing.

Market
Disruption Event             :       The occurrence or existence on any Exchange
                                     Business Day during the one-half hour
                                     period that ends at the close of business
                                     of any suspension of or limitation imposed
                                     on trading (by reason of 
- ----------

 *________* Indicates that material has been omitted and confidential treatment
has been requested therefor. All such omitted material has been filed separately
with Secretary of the Commission in the Company's Application Requesting
Confidential Treatment pursuant to Rule 24b-2 under the Securities Exchange Act
of 1934, as amended.

                                       2
   3

                                     movements in price exceeding levels
                                     permitted by the relevant exchange or
                                     otherwise), provided that any such event is
                                     material in the reasonable determination of
                                     the Calculation Agent, on: (i) the Exchange
                                     in the Shares; or (ii) the Pacific Stock
                                     Exchange in options contracts on the
                                     Shares.

Exchange                     :       Nasdaq National Market

Clearance System
Business Day                 :       Any day on which the Clearance System is
                                     open for the acceptance and execution of
                                     settlement instructions.

Clearance System             :       Depository Trust Company, or any successor
                                     to or transferee of such clearance system.

Calculation Agent            :       Party A, whose calculations shall be
                                     binding absent manifest error.

Procedure for Exercise

Exercise Date                :       The Expiration Date.

Expiration Time              :       5:00 p.m. local time in New York City

Automatic Exercise           :       The Transaction will be deemed to be
                                     automatically exercised if it is
                                     In-the-Money on the Expiration Date, unless
                                     (i) the Buyer has notified the Seller or
                                     its agent (by telephone or in writing)
                                     prior to 5:00 p.m. local time in New York
                                     City on the Expiration Date that it does
                                     not wish to exercise the Transaction; or
                                     (ii) the Closing Value cannot be determined
                                     on the Expiration Date. If the Transaction
                                     is to be cash settled, "In-the-Money" means
                                     that the Cash Settlement Amount is greater
                                     than zero. If the Transaction is to be
                                     physically settled, "In-the-Money" means
                                     that the Closing Value is greater than the
                                     Strike Price. "Closing Value" means the
                                     closing price of the Shares, as reported on
                                     the Exchange, on the Expiration Date.

Telephone or
facsimile number
of Seller's agent
for purposes of
giving notice                :       Telephone:  312-554-5249
                                     Fax:        312-554-6271
                                     Attention:  David P. Stowell

Settlement Terms

Settlement                   :       The Transaction will be cash settled;
                                     provided, however, that Party B may elect
                                     to physically settle the Transaction by
                                     giving notice to Party A no later than
                                     twenty Exchange Business Days before the
                                     Expiration Date.

Physical Settlement          :       If the Transaction is to be physically
                                     settled, on the Settlement Date, the Seller
                                     shall deliver to the Buyer the number of
                                     Shares equal to the Contract Multiplier
                                     multiplied by the number of Options
                                     exercised against payment by the Buyer to
                                     the Seller of an amount equal to the
                                     product of (a) the Strike Price, adjusted
                                     as hereinafter 


                                       3
   4

                                     provided, multiplied by (b) the Contract
                                     Multiplier multiplied by (c) the number of
                                     Options exercised. If the Closing Value
                                     exceeds the Cap Price, the Strike Price
                                     shall be increased by the amount by which
                                     the Closing Value exceeds the Cap Price; if
                                     the Closing Value is equal to or less than
                                     the Cap Price, no adjustment will be made
                                     to the Strike Price. Such payment and such
                                     delivery will be made through the Clearance
                                     System at the accounts specified below, on
                                     a delivery versus payment basis.

Cash Settlement              :       If the Transaction is to be cash settled,
                                     on the Settlement Date, Party A shall pay
                                     to Party B the Cash Settlement Amount, if
                                     any. The "Cash Settlement Amount" shall be
                                     the greater of (a) zero and (b) an amount
                                     calculated by the Calculation Agent equal
                                     to (i) the Contract Multiplier multiplied
                                     by (ii) the number of Options exercised
                                     multiplied by (iii) the Price Differential.
                                     "Price Differential" means (x) if the
                                     Reference Price exceeds the Cap Price, the
                                     result of subtracting the Strike Price from
                                     the Cap Price, and (y) if the Reference
                                     Price is equal to or less than the Cap
                                     Price, the result of subtracting the Strike
                                     Price from the Reference Price.

Reference Price              :       (a) If the Valuation Period contains *__*
                                     Normal Trading Day, the Reference Price
                                     shall be the arithmetic average of the
                                     Share Prices on those *___* Normal Trade
                                     Days.

                                     (b) If the Valuation Period does not
                                     contain *______* Normal Trading Days, the
                                     parties shall jointly determine the Share
                                     Price for the Valuation Date and as many
                                     Exchange Business Days immediately
                                     preceding the Valuation Date as shall be
                                     necessary, when such Share Prices are taken
                                     together with the Share Prices on all
                                     Normal Trading Days occurring within the
                                     Valuation Period, to provide *______* Share
                                     Prices, and in such case the Reference
                                     Price shall be the arithmetic average of
                                     those *_______* Share Prices. If the
                                     parties are unable to reach agreement on
                                     the foregoing determination, then the
                                     parties will negotiate in good faith to
                                     agree on an independent third party that
                                     will make such determination, and, if they
                                     cannot agree within three Exchange Business
                                     Days each of Party A and Party B will
                                     promptly choose an independent third party
                                     and instruct the parties so chosen to agree
                                     on another independent third party that
                                     will make such determination. The
                                     determination of an independent third party
                                     will be binding absent manifest error. The
                                     costs of such independent third party will
                                     be borne equally by Party A and Party B.

Share Price                  :       The closing price of the Shares as reported
                                     on the Exchange.

Valuation Period             :       The period from and including the * ____*
                                     Exchange Business Day immediately preceding
                                     the Expiration Date (the "Initial Date") to
                                     and including the Expiration Date, provided
                                     that if any Exchange Business Day in the
                                     Valuation Period as so determined, shall
                                     not be a Normal Trading Day, the Valuation
                                     Period shall be extended so that the
                                     Valuation Period includes *______* Normal
                                     Trading 

- ----------

 *________* Indicates that material has been omitted and confidential treatment
has been requested therefor. All such omitted material has been filed separately
with Secretary of the Commission in the Company's Application Requesting
Confidential Treatment pursuant to Rule 24b-2 under the Securities Exchange Act
of 1934, as amended.

                                       4
   5


                                     Days, but in no event shall the last day of
                                     the Valuation Period be later than the
                                     *____* Exchange Business Day following the
                                     Expiration Date, and in no event shall the
                                     Valuation Period include any day before the
                                     Initial Date.

Valuation Date               :       The last day of the Valuation Period.

Settlement Date              :       If the Transaction is to be cash settled,
                                     the Settlement Date shall be three Currency
                                     Business Days after the Valuation Date. If
                                     the Transaction is to be physically
                                     settled, the Settlement Date shall be three
                                     Clearance System Business Days after the
                                     Exercise Date.

Adjustment Events

Adjustments                  :       During the life of the Transaction, if any
                                     adjustment is made by The Options Clearing
                                     Corporation or its successors ("OCC") in
                                     the terms of outstanding OCC-issued options
                                     ("OCC Options") on the Shares which are the
                                     subject of the Transactions, an equivalent
                                     adjustment shall be made in the terms of
                                     the Transaction. Except as provided in the
                                     following paragraph and in the "Additional
                                     Adjustment Provisions" below, no adjustment
                                     shall be made in the terms of the
                                     Transaction for any event that does not
                                     result in an adjustment to the terms of
                                     outstanding OCC Options on the Shares.
                                     Without limiting the generality of the
                                     foregoing, NO ADJUSTMENT SHALL BE MADE IN
                                     THE TERMS OF THE TRANSACTIONS FOR ORDINARY
                                     CASH DIVIDENDS ON THE SHARES EXCEPT AS
                                     PROVIDED IN THE "ADDITIONAL ADJUSTMENT
                                     PROVISIONS" BELOW.

                                     If at any time during the life of the
                                     Transaction there shall be no outstanding
                                     OCC Options on the Shares, and an event
                                     shall occur for which an adjustment might
                                     otherwise be made under the By-Laws, Rules,
                                     and stated policies of the OCC applicable
                                     to the adjustment of OCC Options (the "OCC
                                     Adjustment Rules"), the parties shall use
                                     their best efforts, applying the principles
                                     set forth in the OCC Adjustment Rules, to
                                     jointly determine whether to adjust the
                                     terms of the Transaction and the nature of
                                     any such adjustment.

Additional
Adjustments                  :       Notwithstanding the foregoing, if upon the
                                     occurrence of the following events during
                                     the life of the Transaction no adjustment
                                     is required to be made to the terms of the
                                     Transaction in accordance with the
                                     foregoing provisions or if an adjustment
                                     has been made but such adjustment is, in
                                     the determination of the Calculation Agent,
                                     insufficient to preserve the economic
                                     benefit of the Transaction for the parties,
                                     the following additional adjustments shall
                                     be made to the terms of the Transaction:

                                     (a) If (i) an ordinary cash dividend is
                                     declared or paid on the 

- ----------

 *________* Indicates that material has been omitted and confidential treatment
has been requested therefor. All such omitted material has been filed separately
with Secretary of the Commission in the Company's Application Requesting
Confidential Treatment pursuant to Rule 24b-2 under the Securities Exchange Act
of 1934, as amended.

                                       5
   6

                                     Shares or (ii) a special cash dividend is
                                     declared or paid on the Shares and in
                                     either case the Ex-Dividend Date with
                                     respect to such dividend occurs during the
                                     period from, and including, the Effective
                                     Date to, but excluding, the Expiration Date
                                     (each, a "Dividend Event"), the Strike
                                     Price and the Contract Multiplier shall
                                     each be adjusted for each Dividend Event in
                                     accordance with the following formulas:

                                                       SP[0] (CP[0] - DA)
                                                       ------------------ 
                                            SP[1]    =        CP[0]

                                                        SP[0]
                                                       --------
                                            CM[1]    =  SP[1]

                                            Where:

                                     (i) SP[1] = Strike Price after the Dividend
                                                    Event

                                     (ii) CM[1]= Contract Multiplier after the
                                                    Dividend Event

                                     (iii) SP[0] =  Strike Price on the Exchange
                                     Business Day immediately preceding the
                                     Ex-Dividend Date with respect to the
                                     Dividend Event

                                     (iv) CP[0] = The closing price of the 
                                     Shares, as reported on the Exchange, on the
                                     Exchange Business Day immediately preceding
                                     the Ex-Dividend Date with respect to the
                                     Dividend Event

                                     (vi) DA = The amount of the ordinary cash
                                     dividend or the special cash dividend, as
                                     the case may be

                                     (b) If there occurs a tender offer, by the
                                     issuer of the Shares (the "Issuer") or a
                                     third party, for the Shares, and the date
                                     of the expiration of such offer (the
                                     "Termination Date") occurs during the
                                     period from, and including, the Effective
                                     Date to, but excluding, the Expiration Date
                                     (an "Adjustment Event"), the Strike Price
                                     and the Contract Multiplier shall each be
                                     adjusted for each Adjustment Event in
                                     accordance with the following formulas:

                                                          (CP[0] x N[0]) - C
                                                          ----------------
                                     SP[1]      = SP[0] x [CP[0] x (N[0]-N[1])]

                                                  SP[0]
                                                  -----
                                     CM[1]      = SP[1]

                                            Where:

                                     (i)   SP[1] = Strike Price after the
                                           Adjustment Event

                                     (ii)  CM[1] = Contract Multiplier after the
                                           Adjustment Event

                                     (iii) SP[0] = Strike Price on the
                                           Completion Date (as hereinafter 
                                           defined)


                                       6

   7
                                     (iv)   CP[0] = The closing price of the
                                            Shares, as reported on the Exchange,
                                            on the Completion Date

                                     (v)    N[0] = Total number of shares of 
                                            common stock of the Issuer 
                                            outstanding on the Completion Date

                                     (vi)   C = Price paid by the offeror per
                                            share of common stock of the Issuer
                                            multiplied by the total number of
                                            shares purchased by the offeror
                                            pursuant to the Adjustment Event

                                     (vii)  N[1] = Total number of shares of 
                                            common stock of the Issuer purchased
                                            by the offer or pursuant to the 
                                            Adjustment Event

                                     (viii) "Completion Date" means the
                                            Termination Date; provided, however,
                                            that if the period following the
                                            Termination Date within which
                                            delivery of tendered shares may be
                                            guaranteed is less than the
                                            customary settlement period for a
                                            sale of the Shares executed through
                                            the Clearance System, the Completion
                                            Date shall be the date which
                                            precedes the Termination Date by the
                                            number of Exchange Business Days
                                            equal to such difference

Miscellaneous
Transfer              :              Neither party may transfer the Transaction,
                                     in whole or in part, without the prior
                                     written consent of the non-transferring
                                     party.

Account Details

Payments and deliveries to Party A: Previously provided

Payments and deliveries to Party B: Previously provided 


                                       7
   8

Please confirm that the foregoing correctly sets forth the terms of our
agreement by executing the copy of this Confirmation enclosed for that purpose
and returning it to us or by sending to us a letter or telex substantially
similar to this letter, which letter or telex sets forth the material terms of
the Transaction to which this Confirmation relates and indicates your agreement
to those terms.

Yours sincerely,

SWISS BANK CORPORATION, LONDON BRANCH


By:                                            By:
  -------------------------------------           ------------------------------
Name:                                          Name:
Title:                                         Title:



Confirmed as of the ___ day
of ____________, 199__

IDEC PHARMACEUTICALS CORPORATION



By: 
   ------------------------------------
Name:
Title:



                                       8