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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]
                                                                      --------

                                       1

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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.


                                       2

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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
<PAGE>   4
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
                                                             -------------------