Document:

<PAGE>
                                                                    Exhibit 4.4

THIS WARRANT HAS NOT BEEN REGISTERED UNDER THE SECURITIES ACT OF 1933, AS
AMENDED (THE "1933 ACT"), OR ANY APPLICABLE STATE SECURITIES LAWS. AND MAY NOT
BE SOLD OR TRANSFERRED UNLESS SUCH SALE OR TRANSFER IS IN ACCORDANCE WITH THE
REGISTRATION REQUIREMENTS OF SUCH ACT AND APPLICABLE LAWS OR SOME OTHER
EXEMPTION FROM THE REGISTRATION REQUIREMENTS OF SUCH ACT AND APPLICABLE LAWS IS
AVAILABLE WITH RESPECT THERETO.

                          PREFERRED STOCK PURCHASE WARRANT

Warrant No. PSB-1                                     Number of Shares 175,000
                                                      Series B Preferred Stock

                            RIGEL PHARMACEUTICALS, INC.

                             Void after April 30, 2004

     1.   ISSUANCE. This Warrant is issued to LIGHTHOUSE CAPITAL PARTNERS II,
L.P. by RIGEL PHARMACEUTICALS, INC., a Delaware corporation (hereinafter with
its successors called the "COMPANY").

     2.   PURCHASE PRICE; NUMBER OF SHARES. The registered holder of this
Warrant (the "HOLDER"), commencing on the date hereof, is entitled upon
surrender of this Warrant with the subscription form annexed hereto duly
executed, at the principal office of the Company, to purchase from the Company
the following securities (collectively, the "SHARES") at a price per share of
$0.80 (the "PURCHASE PRICE"), 175,000 fully paid and nonassessable shares of
Series B Preferred Stock, $.001 par value, of the Company (the "PREFERRED
STOCK"). Until such time as this Warrant is exercised in full or expires, the
Purchase Price and the securities issuable upon exercise of this Warrant are
subject to adjustment as hereinafter provided. The person or persons on whose
name or names any certificate representing shares of Preferred Stock is issued
hereunder shall be deemed to have become the holder of record of the shares
represented thereby as at the close of business on the date this Warrant is
exercised with respect to such shares, whether or not the transfer books of the
Company shall be closed.

     3.   PAYMENT OF PURCHASE PRICE. The Purchase Price may be paid (i) in cash
or by check, (ii) by the surrender by the Holder to the Company of any
promissory notes or other obligations issued by the Company, with all such notes
and obligations so surrendered being credited against the Purchase Price in an
amount equal to the principal amount thereof plus accrued interest to the date
of surrender, or (iii) by any combination of the foregoing.

     4.   NET ISSUE ELECTION. The Holder may elect to receive, without the
payment by the Holder of any additional consideration, shares of Preferred Stock
equal to the value of this Warrant or any portion hereof by the surrender of
this Warrant or such portion to the Company, with the net issue election notice
annexed hereto duly executed, at the principal office of the Company. Thereupon,
the Company shall issue to the Holder such number of fully paid and
nonassessable shares of Preferred Stock as is computed using the following
formula:

                                 Y (A-B)
                                 ------
                              X=
                                    A

                                       1.

<PAGE>

where:    X =  the number of shares of Preferred Stock to be issued to the
               Holder pursuant to this SECTION 4.

          Y =  the number of shares of Preferred Stock covered by this Warrant
               in respect of which the net issue election is made pursuant to
               this SECTION 4.

          A =  the Fair Market Value (defined below) of one share of Preferred
               Stock, as determined at the time the net issue election is made
               pursuant to this SECTION 4.

          B =  the Purchase Price in effect under this Warrant at the time the
               net issue election is made pursuant to this SECTION 4.

"Fair Market Value" of a share of Preferred Stock (or Common Stock if the
Preferred Stock has been automatically converted into Common Stock) as of a
particular date (the "Determination Date") shall mean:

          (i)  If the net issue election is made in connection with and
     contingent upon the closing of the sale of the Company's Common Stock to
     the public in a public offering pursuant to a Registration Statement under
     the Act (a "Public Offering"), and if the Company's Registration Statement
     relating to such Public Offering ("Registration Statement") has been
     declared effective by the SEC, then the initial "Price to Public" specified
     in the final prospectus with respect to such offering multiplied by the
     number of shares of Common Stock into which each share of Preferred Stock
     is then convertible.

          (ii) If the net issue election is not made in connection with and
     contingent upon a Public Offering, then as follows:

               (A)  If traded on a securities exchange or the Nasdaq National
          Market, the fair market value of the Common Stock shall be deemed to
          be the average of the closing or last reported sale prices of the
          Common Stock on such exchange or market over the 30-day period ending
          five business days prior to the Determination Date, and the fair
          market value of the Preferred Stock shall be deemed to be such fair
          market value of the Common Stock multiplied by the number of shares of
          Common Stock into which each share of Preferred Stock is then
          convertible;

               (B) If otherwise traded in an over-the-counter market, the fair
          market value of the Common Stock shall be deemed to be the average of
          the closing ask prices of the Common Stock over the 30-day period
          ending five business days prior to the Determination Date, and the
          fair market value of the Preferred Stock shall be deemed to be such
          fair market value of the Common Stock multiplied by the number of
          shares of Common Stock into which each share of Preferred Stock is
          then convertible; and

               (C)  If there is no public market for the Common Stock, then fair
          market value shall be determined in good faith by the Company's Board
          of Directors.

     5.   PARTIAL EXERCISE. This Warrant may be exercised in part, and the
Holder shall be entitled to receive a new warrant, which shall be dated as of
the date of this Warrant, covering the number of shares in respect of which this
Warrant shall not have been exercised.

     6.   FRACTIONAL SHARES. In no event shall any fractional share of Preferred
Stock be issued upon any exercise of this Warrant. If, upon exercise of this
Warrant as an entirety, the Holder would, except as provided in this SECTION 6,
be entitled to receive a fractional share of Preferred Stock, then the Company
shall pay in lieu thereof, the Fair Market Value of such fractional share in
cash.

     7.   EXPIRATION DATE; AUTOMATIC EXERCISE. Except as otherwise set forth in
SECTION 11, this Warrant shall expire at the close of business on April 30, 2004
and shall be void thereafter. Notwithstanding the foregoing, this Warrant shall
automatically be deemed to be exercised in full pursuant to the provisions of
SECTION 4 hereof, without

                                       2.

<PAGE>

any further action on behalf of the Holder, immediately prior to the time this
Warrant would otherwise expire pursuant to the preceding sentence or pursuant to
SECTION 11.

     8.   RESERVED SHARES; VALID ISSUANCE. The Company covenants that it will at
all times from and after the date hereof reserve and keep available such number
of its authorized shares of Preferred Stock and Common Stock, $.001 par value,
of the Company (the "COMMON STOCK"), free from all preemptive or similar rights
therein, as will be sufficient to permit, respectively, the exercise of this
Warrant in full and the conversion into shares of Common Stock of all shares of
Preferred Stock receivable upon such exercise. The Company further covenants
that such shares as may be issued pursuant to such exercise and/or conversion
will, upon issuance, be duly and validly issued, fully paid and nonassessable
and free from all taxes, liens and charges with respect to the issuance thereof.

     9.   STOCK SPLITS AND DIVIDENDS. If after the date hereof the Company shall
subdivide the Preferred Stock, by split-up or otherwise, or combine the
Preferred Stock, or issue additional shares of Preferred Stock in payment of a
stock dividend on the Preferred Stock, the number of shares of Preferred Stock
issuable on the exercise of this Warrant shall forthwith be proportionately
increased in the case of a subdivision or stock dividend, or proportionately
decreased in the case of a combination, and the Purchase Price shall forthwith
be proportionately decreased in the case of a subdivision or stock dividend, or
proportionately increased in the case of a combination.

     10.  ADJUSTMENTS FOR DILUTING ISSUANCES. The other antidilution rights
applicable to the Preferred Stock and the Common Stock of the Company are set
forth in the Amended and Restated Certificate of Incorporation, as amended from
time to time (the "Articles"), a true and complete copy in its current form
which is attached hereto as EXHIBIT A. Such rights shall not be restated,
amended or modified in any manner which effects the Holder differently than the
holders of Series B Preferred without such Holder's prior written consent. The
Company shall promptly provide the Holder hereof with any restatement, amendment
or modification to the Articles promptly after the same has been made.

     11.  MERGERS AND RECLASSIFICATIONS. If after the date hereof the Company
shall enter into any Reorganization (as hereinafter defined), then, as a
condition of such Reorganization, lawful provisions shall be made, and duly
executed documents evidencing the same from the Company or its successor
shall be delivered to the Holder, so that the Holder shall thereafter have
the right to purchase, at a total price not to exceed that payable upon the
exercise of this Warrant in full, the kind and amount of shares of stock and
other securities and property receivable upon such Reorganization by a holder
of the number of shares of Preferred Stock which might have been purchased by
the Holder immediately prior to such Reorganization, and in any such case
appropriate provisions shall be made with respect to the rights and interest
of the Holder to the end that the provisions hereof (including without
limitation, provisions for the adjustment of the Purchase Price and the
number of shares issuable hereunder and the provisions relating to the net
issue election) shall thereafter be applicable in relation to any shares of
stock or other securities and property thereafter deliverable upon exercise
hereof. For the purposes of this SECTION 11, the term "REORGANIZATION" shall
include without limitation any reclassification, capital reorganization or
change of the Preferred Stock (other than as a result of a subdivision,
combination or stock dividend provided for in SECTION 9 hereof), or any
consolidation of the Company with, or merger of the Company into, another
corporation or other business organization (other than a merger in which the
Company is the surviving corporation and which does not result in any
reclassification or change of the outstanding Preferred Stock), or any sale
or conveyance to another corporation or other business organization of all or
substantially all of the assets of the Company.

     Notwithstanding the term of this Warrant fixed pursuant to SECTION 7
above and the provisions of this SECTION 11, the right to purchase Preferred
Stock as granted herein shall expire, to the extent not previously exercised,
immediately upon the closing of a merger or consolidation of the Company with
or into another corporation when the Company is not the surviving corporation
(other than a merger or consolidation for the principal purpose of changing
the domicile of the Company), or the sale of all or substantially all of the
Company's capital stock, properties and assets to any other person, in each
case where the stockholders of the Company immediately prior to such merger,
consolidation or sale of assets own (directly or indirectly) less than 50% of
the voting securities of the surviving entity or purchaser of assets in such
transaction (collectively, a "Merger"), except to the extent assumed by the
successor corporation (or parent thereof) in connection with such Merger. In
the event that any outstanding warrants to purchase equity securities of the
Company are assumed, this Warrant shall also be similarly assumed.

                                       3.
<PAGE>

     The Company shall notify the Holder within twenty (20) days of any
proposed Merger, and if the Company fails to deliver such notice, then
notwithstanding anything to the contrary in this Warrant, the rights to
purchase the Company's Preferred Stock (or the shares of stock and other
securities and property receivable upon such Merger by a holder of Preferred
Stock (the "OTHER CONSIDERATION")) shall not expire. The Holder may exercise
the Warrant contingent upon the closing of the Merger. If the Merger does not
close within 60 days after notice, any contingent exercise shall be void.

     12.  CERTIFICATE OF ADJUSTMENT. Whenever the Purchase Price is adjusted,
as herein provided, the Company shall promptly deliver to the Holder a
certificate of the Company's chief financial officer setting forth the
Purchase Price after such adjustment and setting forth a brief statement of
the facts requiring such adjustment.

     13.  NOTICES OF RECORD DATE, ETC. In the event of:

          (a)  any taking by the Company of a record of the holders of any
class of securities for the purpose of determining the holders thereof who
are entitled to receive any dividend or other distribution, or any right to
subscribe for, purchase, sell or otherwise acquire or dispose of any shares
of stock of any class or any other securities or property, or to receive any
other right;

          (b)  any reclassification of the capital stock of the Company,
capital reorganization of the Company, consolidation or merger involving the
Company, or sale or conveyance of all or substantially all of its assets; or

          (c)  any voluntary or involuntary dissolution, liquidation or
winding-up of the Company;

then in each such event the Company will provide or cause to be provided to
the Holder a written notice thereof. Such notice shall be provided at least
twenty (20) business days prior to the date specified in such notice on which
any such action is to be taken.

     14.  REPRESENTATIONS, WARRANTIES AND COVENANTS. This Warrant is issued
and delivered by the Company and accepted by each Holder on the basis of the
following representations, warranties and covenants made by the Company:

          A.   The Company has all necessary authority to issue, execute and
deliver this Warrant and to perform its obligations hereunder. This Warrant
has been duly authorized issued, executed and delivered by the Company and is
the valid and binding obligation of the Company, enforceable in accordance
with its terms, except as enforceability may be limited by bankruptcy,
insolvency, reorganization or other similar laws of general application
affecting the enforcement of Holders rights or by general equity principals
or public policy concerns.

          B.   The shares of Preferred Stock issuable upon the exercise of
this Warrant have been duly authorized and reserved for issuance by the
Company and, when issued in accordance with the terms hereof, will be validly
issued, fully paid and nonassessable.

          C.   The issuance, execution and delivery of this Warrant do not,
and the issuance of the shares of Preferred Stock upon the exercise of this
Warrant in accordance with the terms hereof will not, (i) violate or
contravene the Company's Articles or by-laws, or any law, statute,
regulation, rule, judgment or order applicable to the Company, (ii) violate,
contravene or result in a breach or default under any material contract,
agreement or instrument to which the Company is a party or by which the
Company or any of its assets are bound or (iii) require the consent or
approval of or the filing of any notice or registration with any person or
entity.

          D.   So long as this Warrant has not terminated, Holder shall be
entitled to receive such financial and other information as the Holder would
be entitled to receive under the Series B Preferred Stock Purchase Agreement
if Holder were a holder of that number of shares issuable upon full exercise
of this Warrant.

          E.   As of the date hereof, the authorized capital stock of the
Company consists of (i) 20,000,000 shares of Common Stock, of which 2,510,000
shares are issued and outstanding and 175,000 shares are reserved for

                                      4.
<PAGE>

issuance upon the exercise of this Warrant and the conversion of the Preferred
Stock, (ii) 665,000 shares of Series A Preferred Stock, of which 665,000 are
issued and outstanding shares, and (iii) 7,675,000 shares of Series B Preferred
Stock, of which 7,500,000 are issued and outstanding shares and 175,000 shares
are reserved for issuance upon the exercise of this Warrant. Attached hereto as
EXHIBIT B is a capitalization table summarizing the capitalization of the
Company.

     15.  REGISTRATION RIGHTS. The Company grants to the Holder registration
rights contained in SECTIONS 2.2, 2.3 and 2.4 of the Company's Investor Rights
Agreement dated as of January 17, 1997 (the "INVESTOR RIGHTS AGREEMENT"), so
that (i) the shares of Common Stock issuable upon conversion of the shares of
Preferred Stock issuable upon exercise of this Warrant shall be "Registrable
Securities," and (ii) the Holder shall be a "Holder" and "Investor" for all
purposes of such Investor Rights Agreement.

     16.  AMENDMENT. The terms of this Warrant may be amended, modified or
waived only with the written consent of the Holder.

     17.  REPRESENTATIONS AND COVENANTS OF THE HOLDER. This Preferred Stock
Purchase Warrant has been entered into by the Company in reliance upon the
following representations and covenants of the Holder, which by its execution
hereof the Holder hereby confirms:

          A.   INVESTMENT PURPOSE. The right to acquire Preferred Stock or the
     Preferred Stock issuable upon exercise of the Holder's rights contained
     herein will be acquired for investment and not with a view to the sale or
     distribution of any part thereof, and the Holder has no present intention
     of selling or engaging in any public distribution of the same except
     pursuant to a registration or exemption.

          B.   ACCREDITED INVESTOR. Holder is an "accredited investor" within
the meaning of the Securities and Exchange Rule 501 of Regulation D, as
presently in effect.

          C.   PRIVATE ISSUE. The Holder understands (i) that the Preferred
Stock issuable upon exercise of the Holder's rights contained herein is not
registered under the 1933 Act or qualified under applicable state securities
laws on the ground that the issuance contemplated by this Warrant will be exempt
from the registration and qualifications requirements thereof, and (ii) that the
Company's reliance on such exemption is predicated on the representations set
forth in this SECTION 17.

          D.   FINANCIAL RISK. The Holder has such knowledge and experience in
financial and business matters as to be capable of evaluating the merits and
risks of its investment and has the ability to bear the economic risks of its
investment.

     18.  NOTICES, TRANSFERS, ETC.

          A.   Any notice or written communication required or permitted to be
given to the Holder may be given by certified mail or delivered to the Holder at
the address most recently provided by the Holder to the Company.

          B.   Subject to compliance with applicable federal and state
securities laws, this Warrant may be transferred by the Holder with respect to
any or all of the shares purchasable hereunder. Upon surrender of this Warrant
to the Company, together with the assignment notice annexed hereto duly
executed, for transfer of this Warrant as an entirety by the Holder, the Company
shall issue a new warrant of the same denomination to the assignee. Upon
surrender of this Warrant to the Company, together with the assignment hereof
properly endorsed, by the Holder for transfer with respect to a portion of the
shares of Preferred Stock purchasable hereunder, the Company shall issue a new
warrant to the assignee, in such denomination as shall be requested by the
Holder hereof, and shall issue to such Holder a new warrant covering the number
of shares in respect of which this Warrant shall not have been transferred.

          C.   In case this Warrant shall be mutilated, lost, stolen or
destroyed, the Company shall issue a new warrant of like tenor and denomination
and deliver the same (i) in exchange and substitution for and upon surrender and
cancellation of any mutilated Warrant, or (ii) in lieu of any Warrant lost,
stolen or destroyed, upon receipt

                                       5.

<PAGE>

of an affidavit of the Holder or other evidence reasonably satisfactory to the
Company of the loss, theft or destruction of such Warrant and an indemnification
of loss by the Holder in favor of the Company.

     19.  NO IMPAIRMENT. The Company will not, by amendment of its Articles or
through any reclassification, capital reorganization, consolidation, merger,
sale or conveyance of assets, dissolution, liquidation, issue or sale of
securities or any other voluntary action, avoid or seek to avoid the observance
of performance of any of the terms of this Warrant, but will at all times in
good faith assist in the carrying out of all such terms and in the taking of all
such action as may be necessary or appropriate in order to protect the rights of
the Holder.

     20.  GOVERNING LAW. The provisions and terms of this Warrant shall be
governed by and construed in accordance with the internal laws of the State of
California.

     21.  SUCCESSORS AND ASSIGNS. This Warrant shall be binding upon the
Company's successors and assigns and shall inure to the benefit of the Holder's
successors, legal representatives and permitted assigns.

     22.  BUSINESS DAYS. If the last or appointed day for the taking of any
action required or the expiration of any rights granted herein shall be a
Saturday or Sunday or a legal holiday in California, then such action may be
taken or right may be exercised on the next succeeding day which is not a
Saturday or Sunday or such a legal holiday.

     23.  QUALIFYING PUBLIC OFFERING. If the Company shall effect a firm
commitment underwritten public offering of shares of Common Stock which results
in the conversion of the Preferred Stock into Common Stock pursuant to the
Company's Articles in effect immediately prior to such offering, then, effective
upon such conversion, this Warrant shall change from the right to purchase
shares of Preferred Stock to the right to purchase shares of Common Stock, and
the Holder shall thereupon have the right to purchase; at a total price equal
to that payable upon the exercise of this Warrant in full, the number of shares
of Common Stock which would have been receivable by the Holder upon the exercise
of this Warrant for shares of Preferred Stock immediately prior to such
conversion of such shares of Preferred Stock into shares of Common Stock, and in
such event appropriate provisions shall be made with respect to the rights and
interest of the Holder to the end that the provisions hereof (including, without
limitation, the provisions for the adjustment of the Purchase Price and of the
number of shares purchasable upon exercise of this Warrant and the provisions
relating to the net issue election) shall thereafter be applicable to any shares
of Common Stock deliverable upon the exercise hereof.

     24.  VALUE. The Company and the Holder agree that the value of this Warrant
on the date of grant is $100.

Dated: May     , 1997                  RIGEL PHARMACEUTICALS, INC.
          -----

                                       By:  /s/ NJ Montgomery
                                          -------------------------------
                                       Name:     Nancy Montgomery
                                            -----------------------------
                                       Title:    Chief Financial Officer
                                             ----------------------------

Attest:

     /s/ Brian C. Cunningham
--------------------------------
         Secretary

                                       6.

<PAGE>

                                    SUBSCRIPTION

To:                                       Date:
   ---------------------------------            --------------------------------

     The undersigned hereby subscribes for ___________ shares of Preferred
Stock covered by this Warrant. The certificate(s) for such shares shall be
issued in the name of the undersigned or as otherwise indicated below:

                                  -------------------------------------------
                                  Signature

                                  -------------------------------------------
                                  Name for Registration

                                  -------------------------------------------
                                  Mailing Address

                             NET ISSUE ELECTION NOTICE

To:                                       Date:
   ---------------------------------            --------------------------------

     The undersigned hereby elects under SECTION 4 to surrender the right to
purchase ______ shares of Preferred Stock pursuant to this Warrant. The
certificate(s) for such shares issuable upon such net issue election shall be
issued in the name of the undersigned or as otherwise indicated below:

                                  -------------------------------------------
                                  Signature

                                  -------------------------------------------
                                  Name for Registration

                                  -------------------------------------------
                                  Mailing Address

<PAGE>

                                     ASSIGNMENT

     For value received _______________________________________________ hereby
sells, assigns and transfers unto _____________________________________________
_______________________________________________________________________________
       [Please print or typewrite name and address of Assignee]

_______________________________________________________________________________
the within Warrant, and does hereby irrevocably constitute and appoint
_____________________ its attorney to transfer the within Warrant on the
books of the within named Company with full power of substitution on the
premises.

Dated:
      --------------------

                                      -----------------------------------------

In the Presence of:

----------------------

<PAGE>

                                   EXHIBIT A

               AMENDED AND RESTATED CERTIFICATE OF INCORPORATION

                              SEE ATTACHED PAGES.

<PAGE>

                                   EXHIBIT B

                             CAPITALIZATION TABLE<PAGE>
                                                                    Exhibit 4.5

THIS WARRANT HAS NOT BEEN REGISTERED UNDER THE SECURITIES ACT OF 1933, AS
AMENDED (THE "1933 ACT"), OR ANY APPLICABLE STATE SECURITIES LAWS, AND MAY
NOT BE SOLD OR TRANSFERRED UNLESS SUCH SALE OR TRANSFER IS IN ACCORDANCE WITH
THE REGISTRATION REQUIREMENTS OF SUCH ACT AND APPLICABLE LAWS OR SOME OTHER
EXEMPTION FROM THE REGISTRATION REQUIREMENTS OF SUCH ACT AND APPLICABLE LAWS
IS AVAILABLE WITH RESPECT THERETO.

                          PREFERRED STOCK PURCHASE WARRANT

Warrant No. _________                                  Number of Shares: 131,578
                                                       Series C Preferred Stock

                           RIGEL PHARMACEUTICALS, INC.

                             Void after June 30, 2005

     1.   ISSUANCE. This Warrant is issued to LIGHTHOUSE CAPITAL PARTNERS II,
L.P. by RIGEL PHARMACEUTICALS, INC., a Delaware corporation (hereinafter with
its successors called the "COMPANY").

     2.   PURCHASE PRICE; NUMBER OF SHARES. The registered holder of this
Warrant (the "HOLDER"), commencing on the date hereof, is entitled upon
surrender of this Warrant with the subscription form annexed hereto duly
executed, at the principal office of the Company, to purchase from the
Company the following securities (collectively, the "SHARES") at a price per
share of $1.14 (the "PURCHASE PRICE"), 131,578 fully paid and nonassessable
shares of Series C Preferred Stock, $.001 par value, of the Company (the
"PREFERRED STOCK"). Until such time as this Warrant is exercised in full or
expires, the Purchase Price and the securities issuable upon exercise of this
Warrant are subject to adjustment as hereinafter provided. The person or
persons on whose name or names any certificate representing shares of
Preferred Stock is issued hereunder shall be deemed to have become the holder
of record of the shares represented thereby as at the close of business on
the date this Warrant is exercised with respect to such shares, whether or
not the transfer books of the Company shall be closed.

     3.   PAYMENT OF THE PURCHASE PRICE. The Purchase Price may be paid (i)
in cash or by check, (ii) by the surrender by the Holder to the Company of
any promissory notes or other obligations issued by the Company, with all
such notes and obligations so surrendered being credited against the Purchase
Price in an amount equal to the principal amount thereof plus accrued
interest to the date of surrender, or (iii) by any combination of the
foregoing.

     4.   NET ISSUE ELECTION. The Holder may elect to receive, without the
payment by the Holder of any additional consideration, shares of Preferred
Stock equal to the value of this Warrant or any portion hereof by the
surrender of this Warrant or such portion to the Company, with the net issue
election notice annexed hereto duly executed, at the principal office of the
Company. Thereupon, the Company shall issue to the Holder such number of
fully paid and nonassessable shares of Preferred Stock as is computer using
the following formula:
                                   Y (A - B)
                               X = ---------
                                       A

                                       1.
<PAGE>

where:    X=   the number of shares of Preferred Stock to be issued to the
               Holder pursuant to this SECTION 4.

          Y=   the number of shares of Preferred Stock covered by this Warrant
               in respect of which the net issue election is made pursuant to
               this SECTION 4.

          A=   the Fair Market Value (defined below) of one share of Preferred
               Stock, as determined at the time the net issue election is made
               pursuant to this SECTION 4.

          B=   the Purchase Price in effect under this Warrant at the time the
               net issue election is made pursuant to this SECTION 4.

"Fair Market Value" of a share of Preferred Stock (or Common Stock if the
Preferred Stock has been automatically converted into Common Stock) as a
particular date (the "Determination Date") shall mean:

          (i)  If the net issue election is made in connection with and
     contingent upon the closing of the sale of the Company's Common Stock to
     the public in a public offering pursuant to a Registration Statement under
     the Act (a "Public Offering"), and if the Company's Registration Statement
     relating to such Public Offering ("Registration Statement") has been
     declared effective by the SEC, the initial "Price to Public" specified in
     the final prospectus with respect to such offering multiplied by the number
     of shares of Common Stock into which each share of Preferred Stock is then
     convertible.

          (ii) If the net issue election is not made in connection with and
     contingent upon a Public Offering, then as follows:

               (A)  If traded on a securities exchange or the Nasdaq National
          Market, the fair market value of the Common Stock shall be deemed to
          be the average of the closing or last reported sale prices of the
          Common Stock on such exchange or market over the 30-day period ending
          five business days prior to the Determination Date, and the fair
          market value of the Preferred Stock shall be deemed to be such fair
          market value of the Common Stock multiplied by the number of shares of
          Common Stock into which each share of Preferred Stock is then
          convertible;

               (B)  If otherwise traded in an over-the-counter market, the fair
          market value of the Common Stock shall be deemed to be the average of
          the closing ask prices of the Common Stock over the 30-day period
          ending five business days prior to the Determination Date, and the
          fair market value of the Preferred Stock shall be deemed to be such
          fair market value of the Common Stock multiplied by the number of
          shares of Common Stock into which each share of Preferred Stock is
          then convertible; and

               (C)  If there is no public market for the Common Stock, then fair
          market value shall be determined in good faith by the Company's Board
          of Directors.

     5.   PARTIAL EXERCISE. This Warrant may be exercised in part, and the
Holder shall be entitled to receive a new warrant, which shall be dated as of
the date of this Warrant, covering the number of shares in respect of which
this Warrant shall not have been exercised.

     6.   FRACTIONAL SHARES. In no event shall any fractional share of
Preferred Stock be issued upon any exercise of this Warrant. If, upon
exercise of this Warrant as an entirety, the Holder would, except as provided
in this Section 6, be entitled to receive a fractional share of Preferred
Stock, then the Company shall pay in lieu thereof, the Fair Market Value of
such fractional share in cash.

     7.   EXPIRATION DATE; AUTOMATIC EXERCISE. Except as otherwise set forth
in SECTION 11, this Warrant shall expire at the close of business on June 30,
2005 and shall be void thereafter. Notwithstanding the foregoing, this
Warrant shall automatically be deemed to be exercised in full pursuant to the
provisions of SECTION 4 hereof, without any

                                       2.
<PAGE>

further action on behalf of the Holder, immediately prior to the time this
Warrant would otherwise expire pursuant to the preceding sentence or pursuant
to SECTION 11.

     8.   RESERVED SHARES; VALID ISSUANCE. The Company covenants that it will
at all times from and after the date hereof reserve and keep available such
number of its authorized shares of Preferred Stock and Common Stock, $.001
par value, of the Company (the "COMMON STOCK"), free from all preemptive or
similar rights therein, as will be sufficient to permit, respectively, the
exercise of this Warrant in full and the conversion into shares of Common
Stock of all shares of Preferred Stock receivable upon such exercise. The
Company further covenants that such shares as may be issued pursuant to such
exercise and/or conversion will, upon issuance, be duly and validly issued,
fully paid and nonassessable and free from all takes, liens and charges with
respect to the issuance thereof.

     9.   STOCK SPLITS AND DIVIDENDS. If after the date hereof the Company
shall subdivide the Preferred Stock, by split-up or otherwise, or combine the
Preferred Stock, or issue additional shares of Preferred Stock in payment of
a stock dividend on the Preferred Stock, the number of shares of Preferred
Stock issuable in the exercise of this Warrant shall forthwith be
proportionately increased in the case of a subdivision or stock dividend, or
proportionately increased in the case of a combination, and the Purchase
Price shall forthwith be proportionately decreased in the case of a
subdivision or stock dividend, or proportionately increased in the case of a
combination.

     10.  ADJUSTMENTS FOR DILUTING ISSUANCES. The other antidilution rights
applicable to the Preferred Stock and the Common Stock of the Company are set
forth in the Amended and Restated Certificate of Incorporation, as amended
from time to time (the "Articles"), a true and complete copy in its current
form which is attached hereto as EXHIBIT A. Such rights shall not be
restated, amended or modified in any manner which effects the Holder
differently than the holders of Series C Preferred without such Holder's
prior written consent. The Company shall promptly provide the Holder hereof
with any restatement, amendment or modification to the Articles promptly
after the same has been made.

     11.  MERGERS AND RECLASSIFICATION. If after the date hereof the Company
shall enter into any Reorganization (as hereinafter defined), then, as a
condition of such Reorganization, lawful provisions shall be made, and duly
executed documents evidencing the same from the Company or its successor
shall be delivered to the Holder, so that the Holder shall thereafter have
the right to purchase, at a total price not to exceed that payable upon the
exercise of this Warrant in full, the kind and amount of shares of stock and
other securities and property receivable upon such Reorganization by a holder
of the number of shares of Preferred Stock which might have been purchased by
the Holder immediately prior to such Reorganization, and in any such case
appropriate provisions shall be made with respect to the rights and interest
of the Holder to the end that the provisions hereof (including without
limitation, provisions for the adjustment of the Purchase Price and the
number of shares issuable hereunder and the provisions relating to the net
issue election) shall thereafter be applicable in relation to any shares of
stock or other securities and property thereafter deliverable upon exercise
hereof. For the purposes of this SECTION 11, the term "REORGANIZATION" shall
include without limitation any reclassification, capital reorganization or
change of the Preferred Stock (other than as a result of a subdivision,
combination or stock dividend provided for in SECTION 9 hereof), or any
consolidation of the Company with, or merger of the Company into, another
corporation or other business organization (other than a merger in which the
Company is the surviving corporation and which does not result in any
reclassification or change of the outstanding Preferred Stock), or any sale
or conveyance to another corporation or other business organization of all or
substantially all of the assets of the Company.

     Notwithstanding the term of this Warrant fixed pursuant to SECTION 7
above and the provisions of this SECTION 11, the right to purchase Preferred
Stock as granted herein shall expire, to the extent not previously exercised,
immediately upon the closing of a merger or consolidation of the Company with
or into another corporation when the Company is not the surviving corporation
(other than a merger or consolidation for the principal purpose of changing
the domicile of the Company), or the sale of all or substantially all of the
Company's capital stock, properties and assets to any other person, in each
case where the stockholders of the Company immediately prior to such merger,
consolidation or sale of assets own (directly or indirectly) less than 50% of
the voting securities of the surviving entity or purchaser of assets in such
transaction (collectively, a "Merger"), except to the extent assumed by the
successor corporation (or parent thereof) in connection with such Merger. In
the event that any outstanding warrants to purchase equity securities of the
Company are assumed, this Warrant shall also be similarly assumed.

                                       3.
<PAGE>

     The Company shall notify the Holder within twenty (20) days of any
proposed Merger, and if the Company fails to deliver such notice, then
notwithstanding anything to the contrary in this Warrant, the rights to
purchase the Company's Preferred Stock (or the share of stock and other
securities and property receivable upon such Merger by a holder of the
Preferred Stock (the "OTHER CONSIDERATION")) shall not expire. The Holder may
exercise the Warrant contingent upon the closing of the Merger. If the Merger
does not close within 60 days after notice, any contingent exercise shall be
void.

     12.  CERTIFICATE OF ADJUSTMENT. Whenever the Purchase Price is adjusted,
as herein provided, the Company shall promptly deliver to the Holder a
certificate of the Company's chief financial officer setting forth the
Purchase Price after such adjustment and setting forth a brief statement of
the facts requiring such adjustment.

     13.  NOTICES OF RECORD DATE, ETC. In the event of:

          (a)  any taking by the Company of a record of the holders of any
class of securities for the purpose of determining the holders thereof who
are entitled to receive any dividend or other distribution, or any right to
subscribe for, purchase, sell or otherwise acquire or dispose of any shares
of stock of any class or any other securities or property, or to receive any
other right;

          (b)  any reclassification of the capital stock of the Company,
capital reorganization of the Company, consolidation or merger involving the
Company, or sale or conveyance of all or substantially all of its assets; or

          (c)  any voluntary or involuntary dissolution, liquidation or
winding-up of the Company;

then in such event the Company will provide or cause to be provided to the
Holder a written notice thereof. Such notice shall be provided at least
twenty (20) business days prior to the date specified in such notice on which
any such action is to be taken.

     14.  REPRESENTATIONS, WARRANTIES AND COVENANTS.  This warrant is issued
and delivered by the Company and accepted by each Holder on the basis of the
following representations, warranties and covenants made by the Company:

          A.   The Company has all necessary authority to issue, execute and
deliver this Warrant and to perform its obligations hereunder. This Warrant
has been duly authorized, issued, executed and delivered by the Company and
is the valid and binding obligation of the Company, enforceable in accordance
with its terms, except as enforceability may be limited by bankruptcy,
insolvency, reorganization or other similar laws of general application
affecting the enforcement of Holders rights or by general equity principals
or public policy concerns.

          B.   The shares of Preferred Stock issuable upon the exercise of
this Warrant have been duly authorized and reserved for issuance by the
Company and, when issued in accordance with the terms hereof, will be validly
issued, fully paid and nonassessable.

          C.   The issuance, execution and delivery of this Warrant do not,
and the issuance of the shares of Preferred Stock upon the exercise of this
Warrant in accordance with the terms hereof will not, (i) violate or
contravene the Company's Articles or by-laws, or any law, statute,
regulations, rule, judgment or order applicable to the Company, (ii) violate,
contravene or result in a breach or default under any material contract,
agreement or instrument to which the Company is a party or by which the
Company or any of its assets are bound or (iii) require the consent or
approval of or the filing of any notice or registration with any person or
entity.

          D.   So long as this Warrant has not terminated, Holder shall be
entitled to receive such financial and other information as the Holder would
be entitled to receive under the Series C Preferred Stock Purchase Agreement
if Holder were a holder of that number of shares issuable upon full exercise
of this Warrant.

          E.   As of the date hereof, the authorized capital stock of the
Company consists of (i) 20,000,000 shares of Common Stock, of which 2,510,000
are issued and outstanding shares, 175,000 shares are reserved for

                                       4.
<PAGE>

issuance upon the exercise of that certain Warrant dated May 23, 1997, and
131,578 shares are reserved for issuance upon the exercise of this Warrant
and the conversion of the Preferred Stock, (ii) 665,000 shares of Series A
Preferred Stock, of which 665,000 are issued and outstanding shares, and
(iii) 7,675,000 shares of Series B Preferred Stock, of which 7,500,000 are
issued and outstanding shares, and 175,000 shares are reserved for issuance
upon the exercise of that certain Warrant dated May 23, 1997 and (iv)
8,000,000 shares of Series C Preferred Stock, of which 7,386,843 are issued
and outstanding shares, and 131,578 shares are reserved for issuance upon the
exercise of this Warrant. Attached hereto as EXHIBIT B is a capitalization
table summarizing the capitalization of the Company.

     15.  REGISTRATION RIGHTS.  The Company grants to the Holder registration
rights contained in SECTIONS 2.2, 2.3 and 2.4 of the Company's Amended and
Restated Investor Rights Agreement dated as of November 3, 1997 (the
"INVESTOR RIGHTS AGREEMENT"), so that (i) the shares of Common Stock issuable
upon conversion of the shares of Preferred Stock issuable upon exercise of
this Warrant shall be "Registrable Securities," and (ii) the Holder shall be
a "Holder" and "Investor" for all purposes of such Investor Rights Agreement.

     16.  AMENDMENT. The terms of this Warrant may be amended, modified or
waived only with the written consent of the Holder.

     17.  REPRESENTATIONS AND COVENANTS OF THE HOLDER. The Preferred Stock
Purchase Warrant has been entered into by the Company in reliance upon the
following representations and covenants of the Holder, which by its execution
hereof the Holder hereby confirms:

          A.   INVESTMENT PURPOSE. The right to acquire Preferred Stock or
the Preferred Stock issuable upon exercise of the Holders' rights contained
herein will be acquired for investment and not with a view to the sale or
distribution of any part thereof, and the Holder has not present intention of
selling or engaging in any public distribution of the same except pursuant to
a registration or exemption.

          B.   ACCREDITED INVESTOR. Holder is an "accredited investor" within
the meaning of the Securities and Exchange Rule 501 of Regulation D, as
presently in effect.

          C.   PRIVATE ISSUE. The Holder understands (i) that the Preferred
Stock issuable upon exercise of the Holder's rights contained herein is not
registered under the 1933 Act or qualified under applicable state securities
laws on the ground that the issuance contemplated by this Warrant will be
exempt from the registration and qualifications requirements thereof, and
(ii) that the Company's reliance on such exemption is predicated on the
representations set forth in this SECTION 17.

          D.   FINANCIAL RISK. The Holder has such knowledge and experience
in financial and business matters as to be capable of evaluating the merits
and risks of its investment and has the ability to bear the economic risks of
its investment.

     18.  NOTICES, TRANSFERS, ETC.

          A.   Any notice or written communication required or permitted to
be given to the Holder may be given by certified mail or delivered to the
Holder at the address most recently provided by the Holder to the Company.

          B.   Subject to compliance with applicable federal and state
securities laws, this Warrant may be transferred by the Holder with respect
to any or all of the shares purchasable hereunder. Upon surrender of this
Warrant to the Company, together with the assignment notice annexed hereto
duly executed, for transfer of this Warrant as an entirety by the Holder, the
Company shall issue a new warrant of the same denomination to the assignee.
Upon surrender of this Warrant to the Company, together with the assignment
hereof properly endorsed by the Holder for transfer with respect to a portion
of the shares of the Preferred Stock purchasable hereunder, the Company shall
issue a new warrant to the assignee, in such denomination as shall be
requested by the Holder hereof, and shall issue to such Holder a new warrant
covering the number of shares in respect of which this Warrant shall not have
been transferred.

          C.   In case this Warrant shall be mutilated, lost, stolen or
destroyed, the Company shall issue a new warrant of like tenor and
denomination and deliver the same (i) in exchange and substitution for and
upon surrender

                                       5.
<PAGE>

and cancellation of any mutilated Warrant, or (ii) in lieu of any Warrant
lost, stolen or destroyed, upon receipt of any affidavit of the Holder or
other evidence reasonably satisfactory to the Company of the loss, theft or
destruction of such Warrant and an indemnification of loss by the Holder in
favor of the Company.

     19.  NO IMPAIRMENT. The Company will not, by amendment of its Articles
or through any reclassification, capital reorganization, consolidation,
merger, sale or conveyance of assets, dissolution, liquidation, issue or sale
of securities or any other voluntary action, avoid or seek to avoid the
observance of performance of any of the terms of this Warrant, but will at
all times in good faith assist in the carrying out of all such terms and in
the taking of all such action as may be necessary or appropriate in order to
protect the rights of the Holder.

     20.  GOVERNING LAW. The provisions and terms of this Warrant shall be
governed by and construed in accordance with the internal laws of the State
of California.

     21.  SUCCESSORS AND ASSIGNS. This Warrant shall be binding upon the
Company's successors and assigns and shall inure to the benefit of the
Holder's successors, legal representatives and permitted assigns.

     22.  BUSINESS DAYS. If the last or appointed day for the taking of any
action required or the expiration of any rights granted herein shall be a
Saturday or Sunday or a legal holiday in California, then such action may be
taken or right may be exercised on the next succeeding day which is not a
Saturday or Sunday or such a legal holiday.

     23.  QUALIFYING PUBLIC OFFERING. If the Company shall effect a firm
commitment underwritten public offering of shares of Common Stock which
results in the conversion of the Preferred Stock into Common Stock pursuant
to the Company's Articles in effect immediately prior to such offering, then,
effective upon such conversion, this Warrant shall change from the right to
Purchase shares of Preferred Stock to the right to purchase shares of Common
Stock, and the Holder shall thereupon have the right to purchase, at a total
price equal to that payable upon the exercise of this Warrant in full, the
number of shares of Common Stock which would have been receivable by the
Holder upon the exercise of this Warrant for shares of Preferred Stock
immediately prior to such conversion of such shares of Preferred Stock into
shares of Common Stock, and in such event appropriate provisions shall be
made with respect to the rights and interest of the Holder to the end that
the provisions hereof (including, without limitation, the provisions for the
adjustment of the Purchase Price and of the number of shares purchasable upon
exercise of this Warrant and the provisions relating to the net issue
election) shall thereafter be applicable to any shares of Common Stock
deliverable upon the exercise hereof.

     24.  VALUE. The Company and the Holder agree that the value of this
Warrant on the date of grant is $100.

Dated: July 16, 1998                   RIGEL PHARMACEUTICALS, INC.

                                       By:  /s/ Nancy Montgomery
                                          ------------------------------------

                                       Name:     Nancy Montgomery
                                            ----------------------------------

                                       Title:    Chief Financial Officer
                                             ---------------------------------
Attest:

--------------------------------

                                       6.

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