Document:

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                                                                   EXHIBIT 10.23

                                                                   [DUPONT LOGO]

MASTER LEASE AGREEMENT

Dated and effective as of July 8, 1993 ("Effective Date"), this MASTER LEASE
AGREEMENT ("Agreement") is entered into by and between E.I. Dupont de Nemours &
Co., a Delaware corporation with offices at Barley Mill Plaza 24-2224,
Wilmington, Delaware 19880-0024, (together with any successor or assignee,
"Lessor") and the Lessee indicated below (together with any successor or
permitted assignee, "Lessee").

LESSEE:   LEGAL NAME:                             Signal Pharmaceuticals, Inc.
          TRADE NAME (if any):
          ADDRESS:                                5555 Oberlin Dr
                                                  San Diego, CA 92121

          CONTACT AND TELEPHONE:                  Mark Carman  619-558-7500

          LEGAL ENTITY   Type:                    Corporation

                         State of Organization:   CA

                         Date of Establishment:   7-24-92

LEASE TERMS AND CONDITIONS:

     1.   LEASING. Subject to the terms of this Agreement, Lessor agrees to
lease to Lessee and Lessee agrees to lease from Lessor the equipment
(collectively, the "Equipment" and individually a "unit of Equipment")
described in any equipment schedule (a "Schedule") signed by Lessee and
approved by Lessor. Each Schedule will incorporate all the terms of this
Agreement and will constitute a separate agreement for lease of the Equipment
(each, a "Lease"). With respect to each Lease, capitalized terms not defined in
this Agreement will have the meanings stated in the applicable Schedule. Unless
it purchases the Equipment under Section 14 ("Options"), Lessee does not have
any right or interest in the Equipment except as a lessee. This Agreement is
effective from the Effective Date, and will continue until all Leases have
terminated or expired.

     2.   NET LEASE. EACH LEASE IS A NET LEASE. LESSEE IS UNCONDITIONALLY
OBLIGATED TO PAY MONTHLY RENT AND OTHER AMOUNTS DUE UNDER SUCH LEASE REGARDLESS
OF ANY DEFECT OR DAMAGE TO EQUIPMENT, OR LOSS OF POSSESSION, USE OR DESTRUCTION
FROM ANY CAUSE WHATSOEVER. LESSEE'S OBLIGATIONS CONTINUE UNTIL SPECIFICALLY
TERMINATED AS PROVIDED IN SUCH LEASE. LESSEE IS NOT ENTITLED TO ANY ABATEMENT,
REDUCTION, RECOUPMENT, DEFENSE, OR SET-OFF AGAINST MONTHLY RENT OR OTHER
AMOUNTS DUE TO LESSOR OR ITS ASSIGNEE, WHETHER ARISING OUT OF SUCH LEASE OR OUT
OF LESSOR'S STRICT LIABILITY OR NEGLIGENCE, FROM ANY THIRD PARTY, OR OTHERWISE.

     3.   PURCHASE OF EQUIPMENT. Lessor is not obligated to purchase or lease a
unit of Equipment unless before the Last Funding Date: (i) Lessor receives from
Lessee a fully signed and completed Agreement, a Schedule, and such other
documents as Lessor may require; (ii) Lessor has received from Supplier clear
and unencumbered title to the Equipment; and (iii) there is no Default (Section
13). Provided no Default has occurred, Lessor appoints Lessee as its agent to
inspect and accept the Equipment from Supplier simultaneously with acceptance
of the Equipment for lease hereunder. Unless Lessee advises Lessor in writing
to the contrary within ten (10) days after the date of installation, the
Equipment shall be considered to have been irrevocably accepted by Lessee for
all purposes as of the date of installation. For each Schedule, Lessee
irrevocably authorizes Lessor to adjust the Equipment Price and Total Price by
no more than fifteen percent (15%) to account for equipment change orders or
returns, invoicing errors and similar matters, and agrees to any resulting
adjustments in the TRANSACTION TERMS stated in the applicable Schedule. Lessor
will send Lessee a written notice stating the final Equipment Price, Total
Price and TRANSACTION TERMS, if different from those stated in the applicable
Schedule.

     4.   TERM AND RENT. (a) The Initial Term begins on the acceptance by the
Lessee of the Equipment (a "Lease Commencement Date"), and continues for the
Initial Term stated in the applicable Schedule. The Monthly Rent accrues from
the Lease Commencement Date. Monthly Rent is payable on the same day of each
month as the Lease Commencement Date. If Monthly Rent is not paid within ten
(10) days of its due date, Lessee agrees to pay a late charge of ten cents
(10 cents) per dollar on, and in addition to, such Monthly Rent, but not
exceeding the lawful maximum, if any. Advance Rent, if any, is applied to the
first Monthly Rent due and then to the final Monthly Rents or, at Lessor's
option, to the payment of any overdue obligation of Lessee. Lessor is not
required to: (i) refund any Advance Rent or Monthly Rent; (ii) pay any interest
on Advance Rent; or (iii) keep Advance Rent in a separate account.

     (b) Lessee agrees that the Monthly Rent and Advance Rent have been
calculated on the assumption that the effective corporate income tax rate
(exclusive of any minimum tax rate) for Lessor will be 35%. If Lessor is not
taxed at such tax rate during the Initial Term because of Congressional
enactment of any law, Lessor has the right to increase the Monthly Rent and
Advance Rent and adjust the Casualty Value (Section 8) in such a manner as will
both (i) take into account that such assumption is no longer correct and (ii)
preserve Lessor's after tax economic yields and cash flows. A change in the
Monthly Rent, Advance Rent, or Casualty Value is effective on the effective
date of such law.

     (c) At the end of the term of a Lease, or in the event of a Default, until
Lessee has complied with Section 6(d) ("Use, Operation, Return of Equipment")
or has purchased the Equipment pursuant to Section 14 ("Option"), Lessee shall
pay Lessor Monthly Rent, as liquidated damages for lost rentals and not as a
penalty, such payment to be computed on a daily basis (with one day's rent
being 1/30th of the Monthly Rent) until the Equipment is returned or purchased.
Lessee's obligations and all other provisions of this Lease continue until such
time.

     (d) Notwithstanding anything to the contrary contained herein, during the
first thirty (30) days from and after the Lease Commencement Date (the
"Satisfaction Guaranteed Period"), Lessee may terminate the Lease for any
reason, provided that: (i) Lessor receives written notice of Lessee's intent to
terminate the lease prior to the end of the Satisfaction Guaranteed Period, and
(ii) Lessee makes the Equipment available to Lessor no later than five (5) days
after the date of such notice in the condition required by Section 6(d)(i).
Upon Lessee's compliance with these conditions, Lessor shall refund any Monthly
Rent previously paid by Lessee and Lessee shall have no further obligation as
to the Equipment.

     5.   TAXES. Lessee agrees to pay promptly as additional rent all license
and registration fees and all taxes (excluding taxes on Lessor's net income)
together with penalties and interest (collectively, "Taxes") assessed against
Lessor, Lessee, the applicable Lease, the Equipment, the purchase (including
purchase by Lessee), sale, ownership, delivery, leasing, possession, use,
operation or return of the Equipment or its proceeds (such additional rent,
together with Monthly Rent and Advance Rent is hereinafter collectively
referred to as "Rent"). Where permitted by applicable law, except for Type A
Leases, Lessee will report all Taxes. Lessee will reimburse Lessor on demand
for any Taxes paid by Lessor.

                                                      Lessee Initials [SIG]
                                                                      --------

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     6.   USE, OPERATION, RETURN OF EQUIPMENT. (a) Lessee agrees at its own
expense to: (i) maintain the Equipment in condition suitable for certification
by the manufacturer (if certification is available) and in any event in good
operating condition; (ii) use the Equipment solely for business purposes, in
the manner for which it was intended and in compliance with all applicable
laws and manufacturer requirements or recommendations; (iii) pay all expenses,
fines, and penalties related to the use, operation, condition or maintenance of
the Equipment; and (iv) comply with all license and copyright requirements of
any software ("Software") used in connection with the Equipment.
     (b)  Lessee agrees not to attach to the Equipment any accessory, equipment
or device not leased from Lessor unless it is easily removable without
damaging the Equipment. Lessee agrees to pay all costs for parts, alterations,
and additions to the Equipment (including those required by law), all of which
will become the property of Lessor. lessee agrees not to install any Equipment
or Software, if any, inside any other personal property. Lessor and Lessee
intend that the Equipment is to remain personal property of Lessor.
     (c)  Provided that there is no Default (Section 13), Lessee is authorized
on behalf of Lessor to enforce in its own name (and at its own expense) any
warranty, indemnity or right to damages related to the Equipment which Lessor
has against the Supplier.
     (d)  At the end of the term of a Lease, or in the event of a Default,
Lessee agrees, at its own expense and risk, (i) to pay for any repairs required
to place the Equipment in the same condition as when received by Lessee,
reasonable wear and tear excepted; (ii) without unreasonable delay, to cause
the Equipment to be disassembled, deinstalled, inspected, tested and crated in
accordance with manufacturer recommendations, if any; and (iii) to deliver the
Equipment, freight prepaid, to a carrier selected by Lessor for shipment to a
location selected by Lessor.

     7.   DISCLAIMER. LESSEE AGREES THAT: (1) LESSOR'S ASSIGNEE IS NOT THE
MANUFACTURER OR SUPPLIER OF THE EQUIPMENT OR THE REPRESENTATIVE OF EITHER; (2)
LESSOR'S ASSIGNEE IS NOT REQUIRED TO ENFORCE ANY MANUFACTURER'S WARRANTIES ON
BEHALF OF ITSELF OR OF LESSEE; (3) LESSOR'S ASSIGNEE IS NOT OBLIGATED TO INSPECT
THE EQUIPMENT (4) OTHER THAN AS EXPRESSLY DELIVERED TO LESSEE, LESSOR AND
LESSOR'S ASSIGNEE DO NOT MAKE, AND HAS NOT MADE, ANY WARRANTY OR REPRESENTATION,
EITHER EXPRESS OR IMPLIED, AS TO THE DESIGN, COMPLIANCE WITH SPECIFICATIONS,
OPERATION OR CONDITION OF, OR AS TO THE QUALITY OF THE MATERIAL OR WORKMANSHIP
AS TO THE EQUIPMENT; (5) LESSOR AND LESSOR'S ASSIGNEE DO NOT MAKE ANY WARRANTY
OF MERCHANTABILITY OR FITNESS FOR ANY PARTICULAR PURPOSE OF, OR AS TO TITLE TO,
OR ANY OTHER REPRESENTATION OR WARRANTY, EXPRESS OR IMPLIED, WITH RESPECT TO THE
EQUIPMENT. LESSEE FURTHER AGREES THAT NEITHER LESSOR NOR LESSOR'S ASSIGNEE SHALL
BE LIABLE FOR ANY LIABILITY, LOSS OR DAMAGE CAUSED DIRECTLY OR INDIRECTLY BY THE
EQUIPMENT OR BY ITS INADEQUACY OR BY ANY EQUIPMENT DEFECT, OR ANY FAILURE TO
PROVIDE MAINTENANCE SERVICES, WHETHER OR NOT LESSOR OR ITS ASSIGNEE HAS BEEN
ADVISED OF THE POSSIBILITY OF SUCH LIABILITY, LOSS OR DAMAGE. NEITHER LESSOR NOR
LESSOR'S ASSIGNEE SHALL HAVE ANY LIABILITY TO LESSEE OR ANY OTHER PERSON WITH
RESPECT TO ANY OF THE FOLLOWING, REGARDLESS OF ANY NEGLIGENCE OF LESSOR: (1) THE
USE, OPERATION OR PERFORMANCE OF THE EQUIPMENT; (2) ANY INTERRUPTION OF SERVICE,
LOSS OF BUSINESS OR ANTICIPATED PROFITS OR CONSEQUENTIAL DAMAGES; OR (3) THE
DELIVERY, SERVICING, MAINTENANCE, REPAIR, IMPROVEMENT OR REPLACEMENT OF THE
EQUIPMENT.

     8.   LOSS OR DAMAGE; CASUALTY VALUE. Lessee assumes the risk of any
disappearance of or damage to any part of the Equipment from any cause
whatsoever. Within ten (10) days of learning of any condemnation or other
circumstance where the Equipment is, in Lessee's reasonable opinion,
irreparably damaged or permanently unfit for use ("Casualty") Lessee will
provide Lessor full details of the Casualty and will pay Lessor an amount equal
to (i) the sum of all future Monthly Rents payable for the Equipment under the
applicable Lease, with each such payment discounted to its net present value at
a simple interest rate equal to six percent (6%) per annum (or if not permitted
by applicable law, the lowest permitted rate) from the due date of each such
payment to the Monthly Rate payment date immediately preceding the date of the
Casualty; plus an amount equal to the Casualty Value Percentage of the Total
Price of the Equipment ("Casualty Value"); plus (ii) any other amounts due
under the applicable Lease. Monthly Rent will continue to accrue without
abatement until Lessor receives the Casualty Value and all other amounts
(including Monthly Rent payments) then due under the applicable Lease, at which
time the Lease will terminate. At Lessor's request, Lessee agrees to sell the
Equipment on an "AS IS, WHERE IS" basis without representation or warranty, and
to remit to Lessor any sales or insurance proceeds received (less any sums paid
by Lessee as Casualty Value).

     9.   INSURANCE. Lessee agrees, at its own expense, to keep the Equipment
insured with companies acceptable to Lessor and to maintain primary coverage
consisting of (i) actual cash value all risk insurance on the Equipment, naming
Lessor as loss payee and (ii) single limit public liability and property damage
insurance of not less than $300,000 per occurrence (or such other amounts as
Lessor may require by notice to Lessee) naming Lessee as insured and Lessor as
additional insured. The insurance will provide for not less than thirty (30)
days notice to Lessor of material changes in or cancellation of the policy.
Premiums for all such insurance will be prepaid. Lessee will deliver evidence
of such insurance to Lessor upon request, and will promptly provide to Lessor
all information pertinent to any occurrence which may become the basis of a
claim. Lessee will not make claim adjustments with insurers except with
Lessor's prior written consent.

     10.  REPRESENTATIONS AND WARRANTIES OF LESSEE. Lessee represents and
warrants to Lessor that as of the date of each Lease and of each Certificate of
Acceptance:
     (a)  Lessee has adequate power and capacity to enter into the Lease, any
documents relative to the purchase of the Equipment leased under such Lease and
any other documents required to be delivered in connection with this Lease
(collectively, the "Documents"); the Documents have been duly authorized,
executed and delivered by Lessee and constitute valid, legal and binding
agreements, enforceable in accordance with their terms; there are no
proceedings presently pending or threatened against Lessee which will impair
its ability to perform under the Lease; and all information supplied to Lessor
is accurate and complete.
     (b)  Lessee's entering into the Lease and leasing the Equipment does not
and will not: (i) violate any judgment, order, or law applicable to the Lease,
Lessee or Lessee's certificate of incorporation or by-laws (if Lessee is a
corporation) or Lessee's partnership agreement (if Lessee is a partnership); or
(ii) result in the creation of any lien, security interest or other encumbrance
upon the Equipment.
     (c)  All financial data of Lessee or of any consolidated group of
companies of which Lessee is a member ("Lessee Group"), delivered to Lessor
have been prepared in accordance with generally accepted accounting principles
applied on a consistent basis with prior periods and fairly present the
financial position and results from operations of Lessee, or of the Lessee
Group, as of the stated date and period(s). Since the date of the most recently
delivered financial data, there has been no material adverse change in the
financial or operating condition of Lessee or of the Lessee Group.
     (d)  If Lessee is a corporation or partnership, it is and will be validly
existing and in good standing under laws of the state of its incorporation or
organization; the persons signing the Lease are acting with the full authority
of its board of directors or partners (if Lessee is a partnership) and hold the
offices indicated below their signatures, which are genuine.

     11. LESSEE'S AGREEMENTS. (a) LESSEE AGREES THAT IT WILL KEEP THE EQUIPMENT
FREE AND CLEAR FROM ALL CLAIMS, LIENS AND ENCUMBRANCES AND WILL NOT ASSIGN,
SUBLET, OR GRANT A SECURITY INTEREST IN THE EQUIPMENT OR IN THIS LEASE WITHOUT
LESSOR'S PRIOR WRITTEN CONSENT. If and to the extent that the lease is deemed a
security agreement under the Uniform Commercial Code, and otherwise for
precautionary purposes only, Lessee grants Lessor a first priority security
interest in its interest in the Equipment and in all Equipment leased pursuant
to any schedule. Such security interest shall secure lessee's obligations with
respect to all schedules, leases and agreements between Lessee and Lessor.
Lessee will notify Lessor in writing, with full particulars, within ten (10)
days after it learns of the attachment of any lien to any Equipment and of the
Equipment's location.
     (b)  Lessee will not relocate any unit of Equipment from the Equipment
Location stated on a Schedule without the prior written approval of Lessor
(which shall not be unreasonably withheld). Lessee agrees to notify Lessor
immediately in writing of any change in Lessee's corporate or business name or
in the location of its chief executive office.
     (c)  If this is a Type A Lease, Lessee will not take or fail to take any
action which Lessor determines will result in the disqualification of any
Equipment for, or the recapture of, all or any portion of the accelerated cost
recovery deductions permitted by the Internal Revenue Code of 1986, as amended.
Lessee will indemnify Lessor for any loss in Lessor's after tax economic yields
and cash flows caused by Lessee's acts or failures to act.

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     (d) Lessor may inspect the Equipment during normal business hours. At
Lessor's request, Lessee will attach identifying labels supplied by Lessor
showing Lessor's ownership in a prominent position on each unit of Equipment.

     (e) Within one hundred twenty (120) days of the close of each fiscal year
of Lessee, Lessee will deliver to lessor Lessee's balance sheet and profit and
loss statement, certified by a recognized firm of certified public accountants.
Upon request, Lessee will deliver to Lessor duplicate copies of Lessee's most
recent quarterly financial report.

     12. INDEMNIFICATION. Lessee agrees to indemnify, defend and keep harmless
Lessor, its agents, successors and assigns, from and against any all losses,
damages, penalties, claims and actions, including legal expenses, arising out
of or in connection with (1) the selection, manufacture, purchase, acceptance
or rejection of Equipment, the ownership of Equipment during the term of a
Lease, and the delivery, lease, possession, maintenance, use, condition, return
or operation of equipment or (ii) the condition of Equipment sold or disposed
of after or as a result of use by Lessee or any permitted sublessee of Lessee.

     13. DEFAULT. (a) Lessor may declare a Lease in default (a "Default") if,
with respect to such Lease: (i) Lessor has not received Monthly Rent or any
other Rent (Sections 5 and 15) within ten (10) days after its due date; or (ii)
lessee or any guarantor violates any other term of a lease or any term of a
guaranty and fails to correct such violation within ten (10) days after
written notice from Lessor; or (iii) Lessee violates the terms of any license
or agreement for Software; or (iv) Lessee or any guarantor becomes insolvent,
is liquidated or dissolved, stops doing business or assigns its rights or
property for the benefit of creditors; or (v) a petition is filed by or against
Lessee or any guarantor under Title 11 of the United States Code or any
successor or similar law; or (vi) (for individuals) Lessee or any guarantor
dies or a guardian is appointed for Lessee's or guarantor's person; or (vii)
Lessee (or any affiliate) is in default of or fails to fulfill the terms of any
other agreement between Lessee and Lessor or any affiliate of either.

     (b) At any time after a Default, Lessor may declare a default under any
other Lease or agreement between Lessee (and any affiliate) and Lessor or its
affiliate. Lessor may also enter, with or without legal process, any premises
and take possession of the Equipment. Immediately after a Default, Lessee will
pay to Lessor, as liquidated damages for loss of a bargain and not as a
penalty, an amount equal to the sum of (i) all Rents, including Monthly Rent,
and other sums (e.g. late charges, indemnification, liens) then due under each
Lease; plus (ii) the Casualty Value of the Equipment, calculated as of the
Monthly Rent payment date immediately preceding the Default; together with
interest on such sum accruing to the date of payment at the Overdue Rate
(Section 15). After a Default, at the request of Lessor, Lessee will return the
Equipment as required by Section 6. Lessor may, but is not required to, sell or
lease the Equipment in bulk or in individual pieces. If the Lessor intends to
sell the Equipment, it may do so in a public or private sale and is not
required to give notice of such sale. The Equipment need not be displayed at
the sale. Lessor may, without paying rent or providing insurance, use the
Equipment Location to store the Equipment or conduct any sale. The proceeds of
any sale or lease will be applied in the following order of priorities: (1) to
pay all of Lessor's expenses in taking, removing, holding, repairing and
disposing of Equipment; then (2) to pay any late charges and interest accrued
at the Overdue Rate; then (3) to pay accrued but unpaid Monthly Rent together
with any unpaid Casualty Value, Rent, interest and all other due but unpaid
sums (including any indemnification and sums due under other Leases or
agreements in default). Any remaining proceeds will reimburse Lessee for
payments which it made to reduce the amounts owed to Lessor in the preceding
sentence. Lessor will keep any excess. If the proceeds of any sale or lease are
not enough to pay the amounts owed to Lessor under this Section. Lessee will
pay the deficiency.

     (c) Lessor's remedies for Default may be exercised instead of or in
addition to each other or any other legal or equitable remedies. Lessor has the
right to set-off any sums received from any source (including insurance
proceeds) against Lessee's obligations under each Lease. Lessee waives its
right to object to the notice of the time or place of sale or lease and to the
manner and place of any advertising. Lessee waives any defense based on
statutes of limitations or laches in actions for damages. Lessor's waiver of
any Default is not a waiver of its rights with respect to a different or later
Default.

     14. OPTION. (a) LEASE TYPE A ONLY: So long as no Default has occurred,
Lessee has the option (i) to purchase all but not less than all of the
equipment under a Lease at the end of the Initial Term on an AS-IS-WHERE-IS
basis without representation or warranty, for a cash purchase price equal to
the Equipment's Fair Market Value (plus any applicable sales taxes) determined
as of the end of the Initial Term; or (ii) to extend the Initial Term of a
Lease at the then Fair Market Rental of the Equipment. Lessee must give
irrevocable written notice at least sixty (60) days before the end of the
Initial Term to Lessor that it will purchase the Equipment or extend the
Initial Term. If the Lease is renewed, the Lessee's obligations (other than the
amount of Monthly Rent to be paid) will remain unchanged. "Fair Market Value"
or "Fair Market Rental" means the price or rental which a willing buyer or
lessee (who is neither a lessee in possession nor a used equipment dealer)
would pay for the Equipment in an arm's length transaction to a willing seller
or lessor who is under no compulsion to sell or lease the Equipment. In
determining "Fair Market Value" or "Fair Market Rental": (i) the Equipment is
assumed to have been maintained and returned as required by the Lease; (ii) in
the case of any installed equipment, the Equipment will be valued on an
installed basis; and (iii) cost of removal from the equipment's current
location will not be included.

     (b) LEASE TYPE B ONLY: So long as no Default has occurred, Lessee may
purchase all but not less than all the Equipment under a Lease on a "AS IS,
WHERE IS" basis, without representation or warranty, at the end of the Initial
Term for a price equal to the Option Price (plus applicable sales tax) stated
on a Schedule. Unless the Option Price is $1.00, Lessee must give Lessor
irrevocable written notice at least thirty (30) days before the end of the
Initial Term that it will purchase the Equipment.

     15. ASSIGNMENT. Lessor may, without notice to Lessee, assign its interest
in this Lease, its right to receive Monthly Rent and other sums due hereunder
and its rights in the Equipment. If requested, Lessee agrees to acknowledge, in
writing, any assignment. LESSEE AGREES TO SUCH ASSIGNMENT, AND FURTHER AGREES
THAT, BY SUCH ASSIGNMENT: (1) THE ASSIGNEE SHALL NOT BE CHARGEABLE WITH OR
ASSUME ANY OF THE OBLIGATIONS OR LIABILITIES OF LESSOR, AND (2) THE ASSIGNEE
SHALL HAVE ALL THE RIGHTS AND DISCRETIONS OF LESSOR UNDER THE LEASE, INCLUDING
BUT NOT LIMITED TO THE RIGHT TO ISSUE OR RECEIVE ALL NOTICES OR REPORTS, TO
GIVE ALL CONSENTS, TO RECEIVE TITLE TO THE EQUIPMENT AND TO EXERCISE ALL
REMEDIES THEREUNDER, AND (3) LESSEE SHALL, IN ACCORDANCE WITH THE TERMS OF THIS
LEASE AND ON INSTRUCTION FROM LESSOR, PAY ASSIGNEE ALL RENTS AND OTHER AMOUNTS
DUE UNDER THIS LEASE AS AND WHEN DUE, WITHOUT DEDUCTION OR OFFSET,
NOTWITHSTANDING ANY CLAIM LESSEE MAY HAVE AGAINST LESSOR, OR RELATIVE TO THE
EQUIPMENT, OR ANY OTHER CLAIM OF LESSEE ARISING PRIOR TO THE ASSIGNMENT, AND
(4) LESSEE WILL NOT ASSERT THE ASSIGNEE ANY DEFENSE, CLAIM, COUNTERCLAIM, OR
SET-OFF ON ACCOUNT OF BREACH OF WARRANTY, BREACH OF SERVICE AGREEMENT OR
OTHERWISE IN ANY ACTION FOR RENT OR POSSESSION BROUGHT BY LESSOR'S ASSIGNEE,
AND WILL SETTLE ALL WARRANTY, MECHANICAL, SERVICE, OR OTHER CLAIMS WITH RESPECT
TO THE EQUIPMENT DIRECTLY WITH THE LESSOR AND THAT ASSIGNEE SHALL NOT BE LIABLE
FOR SUCH SERVICE OR OTHER CLAIMS. Lessee may assign this Lese only with the
prior written consent of Lessor or its assignee.

     16. MISCELLANEOUS. (a) LEASE TYPE B ONLY: Lessee agrees that for income
tax purposes only, Lessor is treating Lessee as owner of the Equipment and that
Lessee has not received tax advice from Lessor or the Supplier. By signing this
Lease, Lessee agrees to pay a lease charge and lease charge rate. The total
lease charge is equal to (i) the Monthly Rent multiplied by the number of
months in the Initial Term, plus (ii) the Option Price, minus (iii) the Total
Price. The lease charge portion of the Monthly Rent payments may be determined
by applying to the Total Price of the Equipment the rate which will amortize
such Total Price (adjusting for any Advance Rent) down to the Option Price at a
constant rate over the Initial Term by payment of the Monthly Rent. The lease
charge rate is the constant rate referred to in the preceding sentence. If this
transaction were re-characterized as a financing, no lease charge, late charge,
or post maturity interest charge is intended to exceed the maximum amount of
time price differential or interest, as applicable, permitted to be charged or
collected by applicable law. If this transaction were re-characterized as a
financing and one or more of such charges exceed such maximum, then such
charges will be reduced to the legally permitted maximum charge and any excess
charge will be used to reduce the initial value of the Equipment or refunded.

     (b) Time is of the essence of each Lease. Lessor's failure at any time to
require that Lessee strictly perform its obligations under any Lease will not
prevent Lessor from later requiring such performance. Lessee agrees, upon
Lessor's request, to sign any document presented by Lessor from time to time to
protect Lessor's rights in the Equipment. LESSEE AND LESSOR EACH WAIVE ALL
RIGHTS TO TRIAL BY JURY IN ANY LITIGATION ARISING FROM OR RELATED TO A
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LEASE. Lessee also agrees to pay Lessor's attorneys' fees and out-of-pocket
expenses in protecting or enforcing its rights under a Lease. Lessee will pay
attorney's fees and costs of collection, up to the amount permitted by law.
Lessor and Lessee agree that legal fees and costs up to twenty percent (20%) of
the amount then due under this Lease are reasonable.

     (c)  All required notices will be considered to have been given if sent by
registered or certified mail or overnight courier service to the Lessor at the
address stated above and to the Lessee at its address stated in the Lease, or
at such other place as such addressee may have designated in writing.

     (d)  Each Lease constitutes the entire agreement of the parties with
respect to the lease of the Equipment and supersedes and incorporates all
prior oral or written agreements or statements. So long as there is no Default,
Lessor shall not interfere with Lessee's quiet enjoyment of Equipment. If a
provision of a Lease is declared invalid under law, the affected provision will
be considered omitted or modified to conform to applicable law. All other
provisions will remain in full force and effect.

     (e)  If Lessee fails to comply with any provision of a Lease, Lessor has
the right, but is not obligated, to have such provision brought into
compliance. This right is in addition to the Lessor's right to declare a
Default. All expenses incurred by Lessor in bringing about such compliance will
be considered Rent which is due to Lessor within five (5) days after the date
Lessor sends to Lessee a written request for payment.

     (f)  All overdue payments will bear interest at the Overdue Rate, which is
the lower of twenty percent (20%) per annum or the maximum rate allowed by law.
Interest will accrue daily until payment in full is received.

     (g)  All of Lessor's rights (including indemnity rights) under a Lease
survive the Lease's expiration or termination, and are enforceable by Lessor,
its successors and assigns.

     THIS AGREEMENT AND ANY SCHEDULE AND ANNEXES THERETO CONSTITUTE THE ENTIRE
AGREEMENT OF THE PARTIES WITH RESPECT TO THE SUBJECT MATTER HEREOF. THIS
AGREEMENT IS EFFECTIVE AS OF THE EFFECTIVE DATE UPON SIGNING BY BOTH LESSOR AND
LESSEE. A LEASE MAY NOT BE CHANGED EXCEPT BY WRITTEN AGREEMENT SIGNED BY AN
AUTHORIZED REPRESENTATIVE OF THE PARTY AGAINST WHOM IT IS TO BE ENFORCED.
LESSEE IRREVOCABLY AUTHORIZES LESSOR TO PREPARE AND SIGN ON BEHALF OF LESSEE
ANY INSTRUMENT NECESSARY OR EXPEDIENT FOR FILING, RECORDING OR PERFECTING THE
INTEREST OF LESSOR IN EACH LEASE, THE RELATED EQUIPMENT AND THE PROCEEDS OF
BOTH.

LESSOR:                                 LESSEE:

      E.I. Dupont de Nemours & Co.           Signal Pharmaceuticals, Inc.

By: /s/ KIMBERLY FOX                    By: /s/ MARK D. CARMAN
    --------------------------------        ---------------------------------

Kimberly Fox                            Mark D. Carman
------------------------------------    ------------------------------------
(Print or Type Name)                    (Print or Type Name)

Senior Program Admin.                   V.P. Operations
------------------------------------    ------------------------------------
(Print or Type Title)                   (Print or Type Title)

Date of Execution: 12-27-93             Date of Execution: 12-15-93
                   -----------------                       -----------------

                                        SOCIAL SECURITY OR TAXPAYER
                                        IDENTIFICATION NO:  EIN: 94-3174286
<PAGE>   5

                                                                  [DUPONT LOGO]

Schedule No. 001

MASTER LEASE AGREEMENT EFFECTIVE DATE: JULY 8, 1993

     THIS SCHEDULE ("Schedule") incorporates all of the terms of the above
Master Lease Agreement ("Agreement"). This Schedule and the Agreement as it
relates to this Schedule constitutes a lease ("Lease") for the equipment
described below ("Equipment") between E.I. Dupont de Nemours & Co., ("Lessor")
and the Lessee indicated below. All terms used and not defined in this Schedule
have the definitions stated in the Agreement.

<TABLE>
<S>                           <C>                      <C>
A. LESSEE:                    LEGAL NAME:              Signal Pharmaceuticals, Inc.
                              TRADE NAME (if any):
                              ADDRESS:                 11545 Sorrento Valley Road, Suite 315
                                                       San Diego, CA 92121

                              LEGAL ENTITY - Type:                   Corporation
                                             State of Organization:  CA
                                             Date of Establishment:  7-24-92

B. SUPPLIER:                                           E. I. DUPONT DE NEMOURS & CO.
                                                       MEDICAL PRODUCTS DEPT.
                                                       BARLEY MILL PLAZA
                                                       WILMINGTON DE 19880

C. EQUIPMENT LOCATION:
                              Street Address:          11545 Sorrento Valley Road, Suite 315
                              County:
                              City, State Zip:         San Diego, CA 92121

D. DESCRIPTION OF EQUIPMENT:                           Medical Equipment
</TABLE>

<TABLE>
<CAPTION>
EQUIPMENT TYPE/MODEL                                       NUMBER OF
 SERIAL/ID NUMBERS                                           UNITS                                Cost
--------------------                                       ---------                              ----
<S>                                                           <C>                              <C>
Ultra Centrifuge                                               1                               $73,576.40
Superspeed Centrifuge                                          1
Clinical Centrifuge                                            1

                                                            Equipment Price:                   $73,576.40
                                                                                               ----------
                                                            Sales Tax:                         $ 5,702.17
                                                                                               ----------
                                                            Freight:                           $
                                                                                               ----------
                                                            Installation:                      $
                                                                                               ----------
                                                            Other _____________________:       $
                                                                                               ----------
                                                                Total Price:                   $79,278.57
                                                                                               ----------

E. TRANSACTION TERMS:

     Lease Type (check one):       _____    A  (Tax Lease, ______-year property; all Sections other than 14(b) and 16(a) apply)
                                     X      B  (Lease Purchase all Sections other than 4(b), 11(c) and 14(a) apply).
                                   -----
     Monthly Rent:                 $ See Section F          Advance Rent:                 $

     Sales Tax:                    $                        Sales Tax:                    $

     Total Monthly Rent:           $                        Total Advance Rent:           $

     Initial Term (No. of Months):           060            Casualty Value Percentage:    $      0%

     Last Funding Date:                 12-31-93            Lease Type B Option Price:    $    1.00
</TABLE>

<PAGE>   6

F. ADDITIONAL TERMS (IF ANY):  24 payments @ $947.54, 36 payments @ $2,316.12
                               -------------------------------------------------

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

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

LESSOR:  E.I. DUPONT DE NEMOURS & CO.   LESSEE:  SIGNAL PHARMACEUTICALS, INC.

By: /s/ KIMBERLY FOX                    By: /s/ MARK D. CARMAN
    ---------------------------------       ------------------------------------

    Kimberly Fox                            Mark D. Carman
-------------------------------------   ----------------------------------------
(Print or Type Name)                    (Print or Type Name)

    Senior Program Admin.                   V.P. Operations
-------------------------------------   ----------------------------------------
(Print or Type Title)                   (Print or Type Title)

Date of Approval:  12/27/93             Date of Execution:   12/15/93
-------------------------------------   ----------------------------------------
                                        SOCIAL SECURITY or TAXPAYER
                                        IDENTIFICATION NO.:  EIN: 94-3174286
                                                             -------------------<PAGE>   1
                                                                   EXHIBIT 10.24

                             MASTER EQUIPMENT LEASE

Under this Master Equipment Lease (the "Lease"), dated as of September 1, 1993,
Phoenix Leasing Incorporated ("Lessor") hereby leases to Signal Pharmaceuticals,
Inc. ("Lessee"), and Lessee hereby leases from Lessor, the equipment (herein
called "Equipment") which is described on the schedule attached hereto or any
subsequently-executed schedule entered into by Lessor and Lessee and which
incorporates this Lease by reference. Any such schedules shall hereinafter
individually be referred to as a "Schedule" and collectively be referred to as
the "Schedules." Lessor hereby leases the Equipment to Lessee upon the following
terms and conditions:

      1.    TERM OF AGREEMENT. The term of this Lease begins on the date set
forth above and shall continue thereafter and be in effect so long as and at any
time any Schedule entered into pursuant to this Lease is in effect. The Initial
Term and rent payable with respect to each leased item of Equipment shall be as
set forth in and as stated in the respective Schedule(s). The terms of each
Schedule hereto are subject to all conditions and provisions of this Lease as
may at any time be amended.

      2.    NON-CANCELLABLE LEASE. This Lease and any Schedule cannot be
cancelled or terminated except as expressly provided herein. This Lease
(including all Schedules to this Lease) constitutes a net lease and Lessee
agrees that its obligations to pay all rent and other sums payable hereunder
(and under any Schedule) and the rights of Lessor and assignee in and to such
rent and other sums, are absolute and unconditional and are not subject to any
abatement, reduction, setoff, defense, counterclaim or recoupment due or alleged
to be due to, or by reason of, any past, present or future claims which Lessee
may have against Lessor, any assignee, the manufacturer or seller of the
Equipment, or against any person for any reason whatsoever.

      3.    LESSOR COMMITMENT. So long as no Event of Default or event which
with the giving of notice or passage of time, or both, could become an Event of
Default has occurred or is continuing, Lessor agrees to lease to Lessee the
groups of Equipment described on each Schedule, subject to the following
conditions: (i) that in no event shall Lessor be obligated to lease Equipment to
Lessee hereunder where the aggregate purchase price of all Equipment leased to
Lessee hereunder would exceed $1,000,000 no more than $100,000 of which may be
non-standard equipment and soft costs (such non-standard equipment and soft
costs may not, at any time, constitute greater than 10% of the then aggregate
funding amounts); (ii) the amount of Equipment purchased by Lessor at any one
time shall be at least equal to $50,000 except for a final advance which may be
less than $50,000; (iii) Lessor shall not be obligated to purchase Equipment
hereunder after May 1, 1994; (iv) all Lease documentation required by Lessor has
been executed by Lessee or provided by Lessee no later than October 1, 1993; (v)
the equipment described on the Schedule is acceptable to Lessor; (vi) with
respect to each funding Lessee has provided to Lessor each of the closing
documents described in Exhibit A hereto (which documents shall be in form and
substance acceptable to Lessor) and which list may be modified for each
subsequent funding; (vii) there is no material adverse change in Lessee's
condition, financial or otherwise and Lessee so certifies, from (yy) the date of
the most recent financial statements delivered by Lessee to Lessor prior to
execution of this Lease, to (zz) the date of the proposed lease of the
Equipment; (viii) Lessee is performing according to its business plan dated July
20, 1993 ("Business Plan"), as may be amended from time to time in form and
substance acceptable to Lessor; (ix) Lessor or its agent has inspected and
placed identification labels on the Equipment; (x) Lessee shall offer to Lessor
all lease transactions for Equipment contemplated by Lessee during the
commitment period of this Lease; however if Lessor declines to finance any such
transaction or Lessee and Lessor cannot agree upon terms, then Lessee shall be
free to seek such financing from

                                      -1-
<PAGE>   2
any other third party; and (xi) Lessor has received in form and substance
acceptable to Lessor: (a) Lessee's interim financial statements signed by a
financial officer of Lessee; (b) evidence of Lessee's receipt of $2,100,000
equity; and (c) evidence of Lessee's $699,500 cash position as of July 31, 1993.

      4.    NO WARRANTIES BY LESSOR. (a) Lessee has selected both (i) the
Equipment and (ii) the suppliers (herein called "Vendor") from whom Lessor is to
purchase the Equipment. LESSOR MAKES NO WARRANTY EXPRESS OR IMPLIED AS TO ANY
MATTER WHATSOEVER, INCLUDING THE CONDITION OF THE EQUIPMENT, ITS MERCHANTABILITY
OR ITS FITNESS FOR ANY PARTICULAR PURPOSE, AND AS TO LESSOR, LESSEE LEASES THE
EQUIPMENT "AS IS" AND WITH ALL FAULTS. (b) If the Equipment is not properly
installed, does not operate as represented or warranted by Vendor or is
unsatisfactory for any reason, Lessee shall make any claim on account thereof
solely against Vendor and shall, nevertheless, pay Lessor all rent payable under
this Lease, Lessee hereby waiving any such claims as against Lessor. Lessor
hereby agrees to assign to Lessee solely for the purpose of making and
prosecuting any said claim, to the extent assignable, all of the rights which
Lessor has against Vendor for breach of warranty or other representation
respecting the Equipment. Lessor shall have no responsibility for delay or
failure to fill the order. (c) Lessee understands and agrees that neither the
Vendor nor any salesman or other agent of the Vendor is an agent of Lessor. No
salesman or agent of Vendor is authorized to waive or alter any term or
condition of this Lease, and no representations as to the Equipment or any other
matter by the Vendor shall in any way affect Lessee's duty to pay the rent and
perform its other obligations as set forth in this Lease. (d) Lessee hereby
requests Lessor to purchase Equipment from Vendor and to lease Equipment to
Lessee on the terms and conditions of the Lease set forth herein. (e) Lessee
hereby authorizes Lessor to insert in this Lease and each Schedule hereto the
serial numbers and other identification data of the Equipment when determined by
Lessor.

      5.    LESSEE'S REPRESENTATIONS AND WARRANTIES. Lessee represents and
warrants that (a) it is a corporation in good standing under the laws of the
state of its incorporation, and duly qualified to do business in each state
where the Equipment will be located; (b) it has full authority to execute and
deliver this Lease and perform the terms hereof, and this Lease has been duly
authorized and constitutes valid and binding obligations of Lessee enforceable
in accordance with its terms; (c) this Lease will not contravene any law,
regulation or judgment affecting Lessee or result in any breach of any agreement
or other instrument binding on Lessee; (d) no consent of Lessee's shareholders
or holder of any indebtedness, or filing with, or approval of, any governmental
agency or commission, is a condition to the performance of the terms hereof; (e)
there is no action or proceeding pending or threatened against Lessee before any
court or administrative agency which might have a materially adverse effect on
the business, financial condition or operations of Lessee; (f) no deed of trust,
mortgage or third party interest arising through Lessee will attach to the
Equipment or the Lease; (g) the Equipment will remain at all times under
applicable law, removable personal property, free and clear of any lien or
encumbrance in favor of Lessee or any other person, notwithstanding the manner
in which the Equipment may be attached to any real property; and (h) all credit,
financial and any other information submitted to Lessor herewith or any other
time is true and correct.

      6.    EQUIPMENT ORDERING. Lessee shall be responsible for all packing,
rigging, transportation and installation charges for the Equipment and Lessor
may separately invoice Lessee for such charges. Lessee has selected the
Equipment itself and shall arrange for delivery of Equipment so that it can be
accepted in accordance with Section 7 hereof. Lessee hereby agrees to indemnify
and hold Lessor harmless from any claims,

                                      -2-
<PAGE>   3
liabilities, costs and expenses, including reasonable attorneys' fees, incurred
by Lessor arising out of any purchase orders or assignments executed by Lessor
with respect to any Equipment or services relating thereto.

      7.    LESSEE ACCEPTANCE. Lessee shall return to Lessor the signed and
dated Acceptance Notice attached to each Schedule hereto (a) acknowledging the
Equipment has been received, installed and is ready for use and (b) accepting it
as satisfactory in all respects for the purposes of this Lease. Lessor is
authorized to fill in the Rent Start Date on each Schedule in accordance with
the foregoing.

      8.    LOCATION; INSPECTION; LABELS. Equipment shall be delivered to and
shall not be removed from the Equipment "Location" shown on each Schedule
without Lessor's prior written consent. Lessor shall have the right to inspect
Equipment at any reasonable time. Lessee shall be responsible for all labor,
material and freight charges incurred in connection with any removal or
relocation of such Equipment which is requested by the Lessee and consented to
by Lessor, as well as for any charges due to the installation or moving of the
Equipment. The rental payments shall continue during any period in which the
Equipment is in transit during a relocation. Lessor or its agent shall mark and
label Equipment, which labels shall state Equipment is owned by Lessor, and
Lessee shall keep such labels on the Equipment as labeled by Lessor or its
agent.

      9.    EQUIPMENT MAINTENANCE. (a) General. Lessee will locate or base each
item of Equipment where designated in an Acceptance Notice and will reasonably
permit Lessor to inspect such item of Equipment and its maintenance records.
Lessee will at its sole expense comply with all applicable laws, rules,
regulations, requirements and orders with respect to the use, maintenance,
repair, condition, storage and operation of each item of Equipment. Except as
required herein, Lessee will not make any addition or improvement to any item of
Equipment that is not readily removable without causing material damage to any
item or impairing its original value or utility. Any addition or improvement
that is so required or cannot be so removed will immediately become the property
of Lessor. (b) Service and Repair. With respect to computer equipment, Lessee
has entered into, and will maintain in effect, Vendor's standard maintenance
contract or another contract satisfactory to Lessor for a period equal to the
term of each Schedule and extensions thereto which provides for the maintenance
of the Equipment and repairs and replacement parts thereof in good condition and
working order, all in accordance with the terms of such maintenance contract.
Lessee shall have the Equipment certified for the Vendor's standard maintenance
agreement prior to delivery to Lessor upon expiration of this Lease. With
respect to any other Equipment, Lessee will, at its sole expense, maintain and
service, and repair any damage to, each item of Equipment in a manner consistent
with prudent industry practice and Lessee's own practice so that such item of
Equipment is at all times (i) in the same condition as when delivered to Lessee,
except for ordinary wear and tear, (ii) in good operating order for the function
intended by its manufacturer's warranties and recommendations.

      10.   LOSS OR DAMAGE. Lessee assumes the entire risk of loss to the
Equipment through use, operation or otherwise. Lessee hereby indemnifies and
holds harmless Lessor from and against all claims, loss of rental payments,
costs, damages, and expenses relating to or resulting from any loss, damage or
destruction of the Equipment, any such occurrence being hereinafter called a
"Casualty Occurrence." On the first rental payment date following such Casualty
Occurrence, or, if there is no such rental payment date, thirty (30) days after
such Casualty Occurrence, Lessee shall (i) repair the Equipment, returning it to
good operating condition or (ii) replace the Equipment with identical equipment
in good condition and repair, the title to which shall vest in Lessor and which
thereafter shall be subject to the terms of this Lease; or (iii) pay to Lessor
(a) any

                                      -3-
<PAGE>   4
unpaid amounts relating to such Equipment due Lessor under this Lease up to the
date of the Casualty Occurrence, and (b) a sum equal to the Casualty Value as
set forth in the Casualty Value table attached to each Schedule hereto for such
Equipment. Upon the making of such payment, the term of this Lease as to each
unit of Equipment with respect to which the Casualty Value was paid shall
terminate.

      11.   GENERAL INDEMNITY. Lessee will protect, indemnify and save harmless
Lessor from and against all liabilities, obligations, claims, damages,
penalties, causes of action, costs and expenses, imposed upon or incurred by or
asserted against Lessor or any assignee of Lessor by Lessee or any third party
by reason of the occurrence or existence (or alleged occurrence or existence) of
any act or event relating to or caused by the Equipment, including but not
limited to, consequential or special damages of any kind, or any failure on the
part of Lessee to perform or comply with any of the terms of this Lease. In the
event that any action, suit or proceeding is brought against Lessor by reason of
any such occurrence, Lessee, upon request of Lessor, will at Lessee's expense
resist and defend such action, suit or proceeding or cause the same to be
resisted and defended by counsel designated and approved by Lessor. Lessee's
obligations under this Section 11 shall survive the expiration of this Lease
with respect to acts or events occurring or alleged to have occurred prior to
the return of the Equipment to Lessor at the end of the Lease term.

      12.   INSURANCE. Lessee at its expense shall keep the Equipment insured
for the entire term and any extensions of this Lease against all risks for the
value of the Equipment and in no event for less than the Casualty Value of such
Equipment as specified on Exhibit C. Such insurance shall contain insurer's
agreement to give thirty (30) days written notice to Lessor before cancellation
or material change of any policy of insurance, and shall provide for (a) loss
payable endorsement to Lessor or any assignee of Lessor, and (b) public
liability and property damage insurance in an amount not less than $1,000,000,
naming Lessor as additional insured. Lessee will provide Lessor and any assignee
of Lessor with a certificate of insurance from the insurer evidencing Lessor's
or such assignee's interest in the policy of insurance. Such insurance shall
cover any Casualty Occurrence to any unit of Equipment. Notwithstanding anything
in Section 10 or this Section 12 to the contrary, this Lease and Lessee's
obligations hereunder and under each Schedule shall remain in full force and
effect with respect to any unit of Equipment which is not subject to a Casualty
Occurrence. If Lessee fails to provide or maintain insurance as required herein,
Lessor shall have the right, but shall not be obligated to obtain such
insurance. In that event, Lessee shall pay to Lessor the cost thereof.

      13.   TAXES. Lessee agrees to reimburse Lessor for, (or pay directly if
instructed by Lessor), and agrees to indemnify and hold Lessor harmless from,
all fees (including, but not limited to, license, documentation, recording and
registration fees), and all sales, use, gross receipts, personal property,
occupational, value added or other taxes, levies, imposts, duties, assessments,
charges, or withholdings of any nature whatsoever, together with any penalties,
fines, additions, to tax, or interest thereon (all of the foregoing being
hereafter referred to as "Impositions") except same as may be attributable to
Lessor's income, arising at any time prior to or during the term of this Lease,
or upon termination or early termination of this Lease and levied or imposed
upon Lessor directly or otherwise by any Federal, state or local government in
the United States or by any foreign country or foreign or international taxing
authority upon or with respect to (i) the Equipment, (ii) the exportation,
importation, registration, purchase, ownership, delivery, leasing, possession,
use, operation, storage, maintenance, repair, return, sale, transfer of title,
or other disposition thereof, (iii) the rentals, receipts, or earnings arising
from the Equipment, or any disposition of the rights to such rentals, receipts,
or earnings, (iv) any payment pursuant to this Lease, and (v) this Lease or the
transaction

                                      -4-
<PAGE>   5
or any part thereof. Lessee's obligations under this Section 13 shall survive
the expiration of this Lease with respect to acts or events occurring or alleged
to have occurred prior to the return of the Equipment to Lessor at the end of
the Lease term.

      14.   PAYMENT BY LESSOR. If Lessee shall fail to make any payment or
perform any act required hereunder, then Lessor may, but shall not be required
to, after such notice to Lessee as is reasonable under the circumstances, make
such payment or perform such act with the same effect as if made or performed by
Lessee. Lessee will upon demand reimburse Lessor for all sums paid and all costs
and expenses incurred in connection with the performance of any such act.

      15.   SURRENDER OF EQUIPMENT. Upon termination or expiration of this
Lease, with respect to each group of Equipment, Lessee will forthwith surrender
the Equipment to Lessor delivered in as good order and condition as originally
delivered, reasonable wear and tear excepted. Lessor may, at its sole option,
arrange for removal and transportation of the Equipment provided that Lessee's
obligations under Sections 10, 11 and 12 shall not be released. Lessee shall
bear all expenses of returning (which include, but are not limited to, the
de-installation, insurance, packaging and transportation of) the Equipment to
Lessor's location or other location within the continental United States as
Lessor may request. In the event Lessee fails to return the Equipment as
directed above, all obligations of Lessee under this Lease, including rental
payments, shall remain in full force and effect until Lessee returns the
Equipment to Lessor.

      16.   ASSIGNMENT. WITHOUT LESSOR'S PRIOR WRITTEN CONSENT, LESSEE SHALL NOT
(a) ASSIGN, TRANSFER, PLEDGE, HYPOTHECATE OR OTHERWISE DISPOSE OF THIS LEASE,
EQUIPMENT, OR ANY INTEREST THEREIN, OR (b) SUBLET OR LEND EQUIPMENT OR PERMIT IT
TO BE USED BY ANYONE OTHER THAN LESSEE OR LESSEE'S EMPLOYEES. LESSOR MAY ASSIGN
THIS LEASE OR GRANT A SECURITY INTEREST IN ANY OR ALL EQUIPMENT, OR BOTH, IN
WHOLE OR IN PART TO ONE OR MORE ASSIGNEES OR SECURED PARTIES WITHOUT NOTICE TO
LESSEE. If Lessee is given notice of such assignment it agrees to acknowledge
receipt thereof in writing and Lessee shall execute such additional
documentation as Lessor's assignee shall require. Each such assignee and/or
secured party shall have all of the rights, but none of the obligations, of
Lessor under this Lease, unless such assignee or secured party expressly agrees
to assume such obligations in writing. Lessee shall not assert against any
assignee and/or secured party any defense, counterclaim or offset that Lessee
may have against Lessor. Notwithstanding any such assignment, and providing no
Event of Default has occurred and is continuing, Lessor, or its assignees,
secured parties, or their agents or assigns, shall not interfere with Lessee's
right to quietly enjoy use of Equipment subject to the terms and conditions of
this Lease. Subject to the foregoing, this Lease inures to the benefit of and is
binding upon the successors and assignees of the parties hereto.

      17.   DEFAULT. (a) Event of Default. Any of the following events or
conditions shall constitute an "Event of Default" hereunder: (i) Lessee's
failure to pay any monies due to Lessor hereunder or under any Schedule beyond
the tenth (10th) business day after the same is due; (ii) Lessee's failure to
materially comply with its obligations under Section 12 or Section 16; (iii)
Lessee's failure to comply with or perform any term, covenant, condition,
warranty or representation of this Lease or any Schedule hereto or under any
other agreement between Lessee and Lessor if such failure to comply or perform
is not cured by Lessee within ten (10) days of receipt of notice thereof; (iv)
seizure of the Equipment under legal process; (v) the filing by or against
Lessee of a petition for reorganization or liquidation under the Bankruptcy Code
or any amendment thereto or under any other insolvency law providing for the
relief of debtors; (vi) the voluntary or involuntary making of an assignment of
a substantial portion of its assets by Lessee, or any guarantor under any
guaranty executed in connection with this Lease ("Guaranty"), for

                                      -5-
<PAGE>   6
the benefit of its creditors, the appointment of a receiver or trustee for
Lessee or any Guarantor for any of Lessee's or Guarantor's assets, the
institution by or against Lessee or any Guarantor of any formal or informal
proceeding for dissolution, liquidation, settlement of claims against or winding
up of the affairs of Lessee or any Guarantor; or (vii) the making by Lessee or
any Guarantor of a transfer of all or a material portion of Lessee's or
Guarantor's assets or inventory not in the ordinary course of business. (b)
Remedies. If any Event of Default shall have occurred:

      (i)   Lessor may proceed by appropriate court action or actions either at
law or in equity to enforce performance by Lessee, of the applicable covenants
of this Lease, or to recover damages therefor; or

      (ii)  Lessee will on the next rent payment date following the Event of
Default, pay to Lessor as liquidated damages which the parties agree are fair
and reasonable under the circumstances existing at the time this Lease is
entered into, and not as a penalty, an amount equal to the Casualty Value of
the Equipment set forth in Exhibit C together with any rent or other amounts
past due and owing by Lessee hereunder; or

      (iii) Lessor may, without notice to or demand upon Lessee;

            (a)   Take possession of the Equipment and lease the same or any
portion thereof, for such period, amount, and to such entity as Lessor shall
elect. The proceeds of such lease will be applied by Lessor (A) first, to pay
all costs and expenses, including reasonable legal fees and disbursements,
incurred by Lessor as a result of the default and the exercise of its remedies
with respect thereto, (B) second, to pay Lessor an amount equal to any unpaid
rent or other amounts past due and payable plus the Casualty Value, to the
extent not previously paid by Lessee, and (C) third, to reimburse Lessee for the
Casualty Value to the extent previously paid. Any surplus remaining thereafter
will be retained by Lessor.

            (b)   Take possession of the Equipment and sell the same or any
portion thereof at public or private sale and without demand or notice of
intention to sell. The proceeds of such sale will be applied by Lessor (A)
first, to pay all costs and expenses, including reasonable legal fees and
disbursements, incurred by Lessor as a result of the default and the exercise of
its remedies with respect thereto, (B) second, to pay Lessor an amount equal to
any unpaid rent or other amounts past due and payable plus the Casualty Value,
to the extent not previously paid by Lessee, and (C) third, to reimburse Lessee
for the Casualty Value to the extent previously paid by Lessee. Any surplus
remaining thereafter will be retained by Lessor.

            (c)   Take possession of the Equipment and hold and keep idle the
same or any portion thereof.

            Lessee agrees to pay reasonable internal and out-of-pocket costs of
Lessor related to the exercise of its remedies, including direct costs of its
in-house counsel and out-of-pocket legal fees and expenses. At Lessor's request,
Lessee shall assemble the Equipment and make it available to Lessor at such
location in the continental United States as Lessor may designate. Lessee waives
any right it may have to redeem the Equipment.

                  Repossession of any or all Equipment shall not terminate this
Lease or any Schedule unless Lessor notifies Lessee in writing. Any amount
required to be paid but not paid under this Section shall be increased by a
service charge of 1.5% per month, or

                                      -6-
<PAGE>   7
the highest rate of interest permitted by applicable law, whichever is less,
accruing from the date the Casualty Value or other amounts are payable hereunder
until such amounts are paid.

                  Except as otherwise set forth in this Agreement, none of the
above remedies is intended to be exclusive, but each is cumulative and in
addition to any other remedy available to Lessor, and all may be enforced
separately or concurrently.

                  In addition to the foregoing remedies, if an Event of Default
hereunder shall have occurred and be continuing for a period of 10 business days
without cure, Lessee shall promptly provide Lessor with copies of the minutes of
each meeting of Lessee's board of directors or any committee thereof and copies
of each written consent taken by the board or such committees.

      18.   LATE PAYMENTS. A service charge of 1.5% per month, or the highest
service charge permitted by applicable law, whichever is less, shall be paid by
Lessee to Lessor on all funds owed Lessor by Lessee. If such funds have not been
received by Lessor at Lessor's place of business or by Lessor's designated agent
by the date such funds are due under this Lease, Lessor shall bill Lessee for
such charges. Lessee acknowledges that invoices for rentals due hereunder are
sent by Lessor for Lessee's convenience only. Lessee's non-receipt of an invoice
will not relieve Lessee of its obligation to make rent payments hereunder.

      19.   LESSOR'S EXPENSE. Lessee shall pay Lessor all costs and expenses
including reasonable attorney's fees and the fees of the collection agencies,
incurred by Lessor in enforcing any of the terms, conditions or provisions
hereof.

      20.   OWNERSHIP; PERSONAL PROPERTY. The Equipment shall be and remain
personal property of Lessor, and Lessee shall have no right, title or interest
therein or thereto except as expressly set forth in this Lease, notwithstanding
the manner in which it may be attached or affixed to real property, and upon
termination or expiration of the Lease term, Lessee shall have the duty and
Lessor shall have the right to remove the Equipment from the premises where the
same be located whether or not affixed or attached to the real property or any
building, at the cost and expense of Lessee.

      21.   ALTERATIONS; ATTACHMENTS. No alterations or attachments shall be
made to the Equipment without Lessor's prior written consent, which shall not be
given for changes that will affect the reliability and utility of the Equipment
or which cannot be removed without damage to the Equipment, or which in any way
affect the value of the Equipment for purposes of resale or re-lease.

      22.   FINANCING STATEMENT. Lessee will execute financing statements
pursuant to the Uniform Commercial Code.

      23.   MISCELLANEOUS. (a) Lessee shall provide Lessor with such corporate
resolutions, financial statements, opinions of counsel and other documents as
Lessor shall request from time to time. (b) Lessee represents that the Equipment
is being leased hereunder for business purposes. (c) Time is of the essence with
respect to this Lease. (d) Lessee shall keep its books and records in accordance
with generally accepted accounting principles and practices consistently applied
and shall deliver to Lessor its annual audited financial statements, unaudited
monthly financial statements to include any financial information given to
Lessee's Board of Directors, and signed by an officer of Lessee and such other
unaudited financial statements as may be reasonably requested by

                                      -7-
<PAGE>   8
Lessor. (e) Any action by Lessee against Lessor for any default by Lessor under
this Lease, including breach of warranty or indemnity, shall be commenced within
one (1) year after any such cause of action accrues.

      24.   NOTICES. All notices hereunder shall be in writing, by registered
mail, and shall be directed, as the case may be, to Lessor at 2401 Kerner
Boulevard, San Rafael, California 94901, Attention: Lease Administration and to
Lessee at 11545 Sorrento Valley Road, Suite 315, San Diego, California 92121,
Attention: President.

      25.   ENTIRE AGREEMENT. Lessee acknowledges that Lessee has read this
Lease, understands it and agrees to be bound by its terms, and further agrees
that it and each Schedule constitute the entire agreement between Lessor and
Lessee with respect to the subject matter hereof and supersedes all previous
agreements, promises, or representations. The terms and conditions hereof shall
prevail notwithstanding any variance with the terms of any purchase order
submitted by the Lessee with respect to any Equipment covered hereby.

      26.   AMENDMENT. This Lease may not be changed, altered or modified except
by an instrument in writing signed by an officer of the Lessor and the Lessee.

      27.   WAIVER. Any failure of Lessor to require strict performance by
Lessee or any waiver by Lessor of any provision herein shall not be construed as
a consent or waiver of any other breach of the same or any other provision.

      28.   SEVERABILITY. If any provision of this Lease is held invalid, such
invalidity shall not affect any other provisions hereof.

      29.   JURISDICTION AND WAIVER OF JURY TRIAL. This Lease shall be governed
by and construed under the laws of the State of California. It is agreed that
exclusive jurisdiction and venue for any legal action between the parties
arising out of this Lease shall be in the Superior Court for Marin County,
California, or, in cases where Federal diversity jurisdiction is available, in
the United States District Court for the Northern District of California.
LESSEE, TO THE EXTENT IT MAY LAWFULLY DO SO, HEREBY WAIVES ITS RIGHT TO TRIAL BY
JURY IN ANY ACTION BROUGHT ON OR WITH RESPECT TO THIS LEASE, ANY SCHEDULE, OR
ANY AGREEMENT EXECUTED IN CONNECTION HEREWITH.

      30.   NATURE OF TRANSACTION. Lessor makes no representation whatsoever,
express or implied, concerning the legal character of the transaction evidenced
hereby, for tax or any other purpose.

      31.   SECURITY INTEREST. (a) One executed copy of the Lease will be marked
"Original" and all other counterparts will be duplicates. To the extent, if any,
that this Lease constitutes chattel paper (as such term is defined in the
Uniform Commercial Code as in effect in any applicable jurisdiction) no security
interest in the lease may be created in any documents other than the "Original."
(b) There shall be only one original of each Schedule and it shall be marked
"Original," and all other counterparts will be duplicates. To the extent, if
any, that any Schedule(s) to this Lease constitutes chattel paper (or as such
term is defined in the Uniform Commercial Code as in effect in any applicable
jurisdiction) no security interest in any Schedule(s) may be created in any
documents other than the "Original."

      32.   SUSPENSION OF OBLIGATIONS. The obligations of Lessor hereunder will
be suspended to the extent that it is hindered or prevented from complying
therewith because of labor disturbances, including but not limited to strikes
and lockouts, acts of God,

                                      -8-
<PAGE>   9
fires, storms, accidents, failure of the manufacturer to deliver any item of
Equipment, governmental regulations or interference, or any cause whatsoever not
within the sole and exclusive control of Lessor.

      33.   COMMITMENT FEE. Lessee has paid to Lessor a commitment fee ("Fee")
of $10,000. The Fee shall be applied by Lessor first to reimburse Lessor for all
out-of-pocket UCC search costs incurred by Lessor, and then proportionally to
the first and second months' rent for each Schedule hereunder in the proportion
that the purchase price of the Equipment leased pursuant to the Schedule bears
to Lessor's entire commitment. However, the portion of the Fee which is not
applied to rental shall be non-refundable except if Lessor defaults in its
obligations pursuant to Section 3.

      37.   FINANCE LEASE. The parties agree that this lease is a "Finance
Lease" as defined by section 10-103(a)(7) of the California Commercial Code
(Cal.Com.C.). Lessee acknowledges either (a) that Lessee has reviewed and
approved any written Supply Contract (as defined by Cal.Com.C. Section
10-103(a)(25)) covering Equipment purchased from the "Supplier" (as defined by
Cal.Com.C. Section 10-103(a)(24)) thereof for lease to Lessee or (b) that Lessor
has informed or advised Lessee, in writing, either previously or by this Lease
of the following: (i) the identity of the Supplier; (ii) that the Lessee may
have rights under the Supply Contract; and (iii) that the Lessee may contact the
Supplier for a description of any such rights Lessee may have under the Supply
Contract. Lessee hereby waives any rights and remedies Lessee may have under
Cal.Com.C. Sections 10-508 through 522.

      IN WITNESS WHEREOF, the parties hereto have executed this Lease.

PHOENIX LEASING INCORPORATED           SIGNAL PHARMACEUTICAL, INC.

By: [SIG]                              By: /s/ MARK D. CARMAN
    -----------------------------          -------------------------------------

Title: V.P.                            Title: V.P. Operations & Corp. Develop.
       --------------------------             ----------------------------------

Exhibit A - Closing Memorandum

                                      -9-
<PAGE>   10
                                                 Exhibit A
                                                 to MASTER EQUIPMENT LEASE
                                                 Dated September 1, 1993

                               CLOSING MEMORANDUM

1.    Duly Executed Equipment Lease marked "Original."

2.    Duly Executed Schedule marked "Original."

3.    Duly Executed Certificate of Acceptance.

5.    Insurance Certificates.

6.    Resolutions of Lessee's Board of Directors/Incumbency Certificate.

7.    Consent to Removal of Personal Property.

8.    Purchase Agreement Assignment (if applicable).

9.    UCC Financing Statements.

10.   Bill of Sale (for Sale-Leaseback Equipment) (if applicable).

11.   UCC search.

12.   Equipment List, in form and substance satisfactory to Lessor.

13.   Certificate of Chief Financial Officer as to the existence of no defaults
      and as to there being no material adverse change in the condition,
      financial or otherwise, of the Lessee.

                                      -10-
<PAGE>   11
                               ACCEPTANCE NOTICE
                                   SCHEDULE 1

Reference is made to the Master Equipment Lease dated as of September 1, 1993
between Phoenix Leasing Incorporated as Lessor and Signal Pharmaceuticals, Inc.
as Lessee (the "Lease").

Lessee confirms that the following Equipment has been received, installed and
is ready for use by Lessee. The Equipment is satisfactory in all respects for
the purposes of this Lease as of the date Lessee executes this Notice below.

<TABLE>
<CAPTION>
Description of
Equipment
(quantity, model           Purchase                           Mfr./
and serial number)         Price             Rent             Vendor         Location
------------------         --------          ----             ------         --------
<S>                        <C>               <C>              <C>            <C>

Total:                     $                 $
</TABLE>

THE LEASE MAY NOT BE CHANGED, ALTERED OR MODIFIED EXCEPT BY AN INSTRUMENT IN
WRITING SIGNED BY AN OFFICER OF LESSOR AND A DULY AUTHORIZED REPRESENTATIVE OF
LESSEE.

IN WITNESS WHEREOF, Lessee has executed this Acceptance Notice as of
November 1, 1993.

                                        SIGNAL PHARMACEUTICALS, INC.

                                        By:     /s/ Mark D. Carman
                                           ------------------------------------

                                        Name:   MARK D. CARMAN
                                             ----------------------------------

                                        Title:  V.P. OPERATIONS
                                              ---------------------------------

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