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                                                                   EXHIBIT 10.12

                                                                    CONFIDENTIAL

                         [CB RICHARD ELLIS LETTERHEAD]

ARTICLE 1 BASIC TERMS

                  This Article One contains the Basic Terms of this Lease
between the Landlord and Tenant named below. Other Articles, Sections and
Paragraphs of the Lease referred to in this Article One explain and define the
Basic Terms and are to be read in conjunction with the Basic Terms.

         Section 1.01. DATE OF LEASE: January 1, 2002

         Section 1.02. LANDLORD (INCLUDE LEGAL ENTITY): Church Ranch Business
Center, LLC

Address of Landlord: 10050 Wadsworth Blvd., Westminster, Colorado 80021

         Section 1.03. TENANT (INCLUDE LEGAL ENTITY): Myogen, Inc.

Address of Tenant: 7577 West 103rd Avenue, Suite 212, Westminster, Colorado
80021

         Section 1.04. PROPERTY: The Property is part of Landlord's multi-tenant
real property development known as Church Ranch Business Center LLC (the
"Project"). The Property is depicted on Exhibit A to this Lease. The Project
includes the land, the buildings and all other improvements located on the land,
and the common areas described in Paragraph 4.05(a) and is depicted in Exhibit
F. The Property is (include street address, approximate square footage and
description) Church Ranch Business Center, 7575 and 7577 West 103rd Avenue
Building 2 - suites 209 - 212, Building 1 - suites 102 - 107), Suite 102 & 212,
Westminster, Colorado 80021 totaling 22,040 total gross square feet.

         Section 1.05. LEASE TERM: Approximately 5 years 2 months BEGINNING ON
January 12, 2002 or such other date as is specified in this Lease, and ENDING ON
February 28, 2007.

         Section 1.06. PERMITTED USES: (See Article Five) Office and Research &
Development (Laboratory Facility).

         Section 1.07. TENANT'S GUARANTOR: (If none, so state) None

         Section 1.08. BROKERS: (See Article Fourteen) (If none, so state)

Landlord's Broker: None

Tenant's Broker: None

         Section 1.09. COMMISSION PAYABLE TO LANDLORD'S BROKER: (See Article
Fourteen) None

         Section 1.10 INITIAL SECURITY DEPOSIT: (See Section 3.03) $27,299.15
(or an additional $14,546.25)

         Section 1.11 VEHICLE PARKING SPACES ALLOCATED TO TENANT: (See Section
4.05) 3.92 spaces Per 1,000 SF or 86 spaces.

         Section 1.12 RENT AND OTHER CHARGES PAYABLE BY TENANT: Cancellation
Option 2-28-05, Penalty $62,404.10.

         (a) BASE RENT: See attached exhibit A Dollars ($23,748.10) per month
for the first 38 months, and shall be increased on the first day of the 39th
month(s) after the Commencement Date to $25,713.33 per month through end of
lease term.

         (b) OTHER PERIODIC PAYMENTS: (i) Real Property Taxes (See Section
4.02); (ii) Utilities (See Section 4.03); (iii) Insurance Premiums (See Section
4.04); (iv) Tenant's Initial Pro Rata Share of Common Area Expenses 17.4% of the
entire 126,550 square feet (See Section 4.05); (v) Impounds for Insurance
Premiums and Property Taxes (See Section 4.08); (vi) Maintenance, Repairs and
Alterations (see Article Six).

         Section 1.13 LANDLORD'S SHARE OF PROFIT ON ASSIGNMENT OR SUBLEASE: (See
Section 9.05) zero percent (0% of the entire 126,550 SF) of the Profit (the
"Landlord's Share").

         Section 1.14 RIDERS: The following Riders are attached to and made a
part of this Lease: (If none, so state) Exhibits A, B, C, D, E, F, and G.

ARTICLE 2 LEASE TERM

         Section 2.01. LEASE OF PROPERTY FOR LEASE TERM. Landlord leases the
Property to Tenant and Tenant leases the Property from Landlord for the Lease
Term. The Lease Term is for the period stated in Section 1.05 above and shall
begin and end on the dates specified in Section 1.05 above, unless the beginning
or end of the Lease Term is changed under any provision of this Lease. The
"Commencement Date" shall be the date specified in Section 1.05 above for the
beginning of the Lease Term, unless advanced or delayed under any provision of
this Lease.

         Section 2.02. DELAY IN COMMENCEMENT. Landlord shall not be liable to
Tenant if Landlord does not deliver possession of the Property to Tenant on the
Commencement Date. Landlord's non-delivery of the Property to Tenant on that
date shall not affect this Lease or the obligations of Tenant under this Lease
except that the Commencement Date shall be delayed until Landlord delivers
possession of the Property to Tenant and the Lease Term shall be extended for a
period equal to the delay in delivery of possession of the Property to Tenant,
plus the number of days necessary to end the Lease Term on the last day of a
month. If Landlord does not deliver possession of the Property to Tenant within
sixty (60) days after the Commencement Date, Tenant may elect to cancel this
Lease by giving written notice to Landlord within ten (10) days after the sixty
(60) -day

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period ends. If Tenant gives such notice, the Lease shall be canceled and
neither Landlord nor Tenant shall have any further obligations to the other. If
Tenant does not give such notice, Tenant's right to cancel the Lease shall
expire and the Lease Term shall commence upon the delivery of possession of the
Property to Tenant. If delivery of possession of the Property to Tenant is
delayed, Landlord and Tenant shall, upon such delivery, execute an amendment to
this Lease setting forth the actual Commencement Date and expiration date of the
Lease. Failure to execute such amendment shall not affect the actual
Commencement Date and expiration date of the Lease.

         Section 2.03. EARLY OCCUPANCY. If Tenant occupies the Property prior to
the Commencement Date, Tenant's occupancy of the Property shall be subject to
all of the provisions of this Lease. Early occupancy of the Property shall not
advance the expiration date of this Lease. Tenant shall pay Base Rent and all
other charges specified in this Lease for the early occupancy period.

         Section 2.04. HOLDING OVER. Tenant shall vacate the Property upon the
expiration or earlier termination of this Lease. Tenant shall reimburse Landlord
for and Indemnify Landlord against all damages which Landlord incurs from
Tenant's delay in vacating the Property. If Tenant does not vacate the Property
upon the expiration or earlier termination of the Lease and Landlord thereafter
accepts rent from Tenant, Tenant's occupancy of the Property shall be a
"month-to-month" tenancy, subject to all of the terms of this Lease applicable
to a month-to-month tenancy, except that the Base Rent then in effect shall be
increased by twenty-five percent (25%).

ARTICLE 3 BASE RENT

         Section 3.01. TIME AND MANNER OF PAYMENT. Upon execution of this Lease,
Tenant shall pay Landlord the Base Rent in the amount stated In Exhibit A for
the first month of the Lease Term. On the first day of the second month of the
Lease Term and each month thereafter, Tenant shall pay Landlord the Base Rent,
in advance, and except as set forth in this Lease, payment of Base Rent shall be
without offset, deduction or prior demand. The Base Rent shall be payable at
Landlord's address or at such other place as Landlord may designate in writing.

         Section 3.03. SECURITY DEPOSIT; INCREASES.

         (a) Upon the execution of this Lease, Tenant shall deposit with
Landlord a cash Security Deposit in the amount set forth in Section 1.10 above.
Landlord may apply all or part of the Security Deposit to any unpaid rent or
other charges due from Tenant or to cure any other defaults of Tenant. If
Landlord uses any part of the Security Deposit, Tenant shall restore the
Security Deposit to its full amount within ten (10) days after Landlord's
written request. Tenant's failure to do so shall be a material default under
this Lease. No interest shall be paid on the Security Deposit. Landlord shall
not be required to keep the Security Deposit separate from Its other accounts
and no trust relationship is created with respect to the Security Deposit.

         (b) Each Time the Base Rent is increased, Tenant shall deposit
additional funds with Landlord sufficient to increase the Security Deposit to an
amount which bears the same relationship to the adjusted Base Rent as the
initial Security Deposit bore to the Initial Base Rent.

         Section 3.04. TERMINATION; ADVANCE PAYMENTS. Upon termination of this
Lease under Article Seven (Damage or Destruction), Article Eight (Condemnation)
or any other termination not resulting from Tenant's default, and after Tenant
has vacated the Property in the manner required by this Lease, Landlord shall
refund or credit to Tenant (or Tenant's successor) the unused portion of the
Security Deposit, any advance rent or other advance payments made by Tenant to
Landlord, and any amounts paid for real property taxes and other reserves which
apply to any time periods after termination of the Lease.

ARTICLE 4 OTHER CHARGES PAYABLE BY TENANT

         Section 4.01. ADDITIONAL RENT. All charges payable by Tenant other than
Base Rent are called "Additional Rent." Unless this Lease provides otherwise,
Tenant shall pay all Additional Rent then due with the next monthly installment
of Base Rent. The term "rent" shall mean Base Rent and Additional Rent.

         Section 4.02. PROPERTY TAXES.

         (a) Tenant shall pay all real property taxes on the Property (including
any fees, taxes or assessments against, or as a result of, any tenant
improvements installed on the Property by or for the benefit of Tenant) during
the Lease Term. Subject to Paragraph 4.02(c) and Section 4.08 below, such
payment shall be made at least ten (10) days prior to the delinquency date of
the taxes. Within such ten (10) -day period, Tenant shall furnish Landlord with
satisfactory evidence that the real property taxes have been paid. Landlord
shall reimburse Tenant for any real property taxes paid by Tenant covering any
period of time prior to or after the Lease Term. If Tenant fails to pay the real
property taxes when due, Landlord may pay the taxes and Tenant shall reimburse
Landlord for the amount of such tax payment as Additional Rent.

         (b) DEFINITION OF "REAL PROPERTY TAX." "Real property tax" means: (i)
any fee, license fee, license tax, business license fee, commercial rental tax,
levy, charge, assessment, or tax imposed by any taxing authority against the
Property; (ii) any tax on the Landlord's right to receive, or the receipt of,
rent or income from the Property or against Landlord's business of leasing the
Property; (iii) any tax or charge for fire protection, streets, sidewalks, road
maintenance, refuse or other services provided to the Property by any
governmental agency, (iv) any tax imposed upon this transaction or based upon a
re-assessment of the Property due to a change of ownership, as defined by
applicable law, or other transfer of all or part of Landlord's interest in the
Property; and (v) any charge or fee replacing any tax previously included within
the definition of real property tax. "Real property tax" does not, however,
include Landlord's federal or state income, franchise, inheritance or estate
taxes.

         (c) JOINT ASSESSMENT. If the Property is not separately assessed,
Landlord shall reasonably determine Tenant's share of the real property tax
payable by Tenant under Paragraph 4.02(a) from the assessor's worksheets or
other reasonably

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available information. Tenant shall pay such share to Landlord within fifteen
(15) days after receipt of Landlord's written statement.

         (d) PERSONAL PROPERTY TAXES.

         (i) Tenant shall pay all taxes charged against trade fixtures,
furnishings, equipment or any other personal property belonging to Tenant.
Tenant shall try to have personal property taxed separately from the Property.

         (ii) If any of Tenant's personal property is taxed with the Property,
Tenant shall pay Landlord the taxes for the personal property within fifteen
(15) days after Tenant receives a written statement from Landlord for such
personal property taxes.

         Section 4.03. UTILITIES. Landlord shall assure that the Property is
supplied with, and, Tenant shall pay, directly to the appropriate supplier, the
cost of all natural gas, heat, light, power, sewer service, telephone, water,
refuse disposal and other utilities and services supplied to the Property.
However, if any services or utilities are jointly metered with other property,
Landlord shall make a reasonable determination of Tenant's proportionate share
of the cost of such utilities and services and Tenant shall pay such share to
Landlord within fifteen (15) days after receipt of Landlord's written statement.

         Section 4.04. INSURANCE POLICIES.

         (a) LIABILITY INSURANCE. During the Lease Term, Tenant shall maintain a
policy of commercial general liability insurance (sometimes known as broad form
comprehensive general liability insurance) insuring Tenant against liability for
bodily injury, property damage (including loss of use of property) and personal
injury arising out of the operation, use or occupancy of the Property. Tenant
shall name Landlord as an additional insured under such policy. The initial
amount of such insurance shall be One Million Dollars ($1,000,000) per
occurrence and shall be subject to periodic increase based upon inflation,
increased liability awards, recommendation of Landlord's professional insurance
advisers and other relevant factors. The liability insurance obtained by Tenant
under this Paragraph 4.04(a) shall (i) be primary and non-contributing; (ii)
contain cross-liability endorsements; and (iii) insure Landlord against Tenant's
performance under Section 5.05, if the matters giving rise to the indemnity
under Section 5.05 result from the negligence of Tenant. The amount and coverage
of such insurance shall not limit Tenant's liability nor relieve Tenant of any
other obligation under this Lease. Landlord may also obtain comprehensive public
liability insurance in an amount and with coverage determined by Landlord
insuring Landlord against liability arising out of ownership, operation, use or
occupancy of the Property. The policy obtained by Landlord shall not be
contributory and shall not provide primary insurance. (See additional provisions
in Exhibit D)

         (b) PROPERTY AND RENTAL INCOME INSURANCE. During the Lease Term,
Landlord shall maintain policies of insurance covering loss of or damage to the
Property in the full amount of its replacement value (See Exhibit E for
definition of Landlord's work). Such policy shall contain an Inflation Guard
Endorsement. and shall provide protection against all perils included within the
classification of fire, extended coverage, vandalism, malicious mischief,
special extended perils (all risk), sprinkler leakage and any other perils which
Landlord deems reasonably necessary. Landlord shall have the right to obtain
flood and earthquake insurance if required by any lender holding a security
interest in the Property. Landlord shall not obtain insurance for Tenant's
fixtures or equipment or building improvements installed by Tenant on the
Property. During the Lease Term, Landlord shall also maintain a rental income
insurance policy, with loss payable to Landlord, in an amount equal to one
year's Base Rent, plus estimated real property taxes and insurance premiums.
Tenant shall be liable for the payment of Tenant's pro rata share of any
deductible amount under Landlord's or Tenant's insurance policies maintained
pursuant to this Section 4.04, in an amount not to exceed Ten Thousand Dollars
($10,000). Tenant shall not do or permit anything to be done which invalidates
any such insurance policies.

         (c) PAYMENT OF PREMIUMS. Subject to Section 4.08, Tenant shall pay all
premiums for the Insurance policies described in Paragraphs 4.04(a) and (b)
(whether obtained by Landlord or Tenant) within fifteen (15) days after Tenant's
receipt of a copy of the premium statement or other evidence of the amount due,
except Landlord shall pay all premiums for non-primary comprehensive public
liability insurance which Landlord elects to obtain as provided in Paragraph
4.04(a). For insurance policies maintained by Landlord which cover improvements
on the entire Project, Tenant shall pay Tenant's prorated share of the premiums,
in accordance with the formula In Paragraph 4.05(e) for determining Tenant's
share of Common Area cost. If insurance policies maintained by Landlord cover
improvements on real property other than the Project, Landlord shall deliver to
Tenant a statement of the premium applicable to the Property showing in
reasonable detail how Tenant's share of the premium was computed. If the Lease
Term expires before the expiration of an insurance policy maintained by
Landlord, Tenant shall be liable for Tenant's prorated share of the insurance
premiums. Before the Commencement Date, Tenant shall deliver to Landlord a copy
of any policy of insurance which Tenant is required to maintain under this
Section 4.04. At least thirty (30) days prior to the expiration of any such
policy, Tenant shall deliver to Landlord a renewal of such policy. As an
alternative to providing a policy of insurance, Tenant shall have the right to
provide Landlord a certificate of insurance, executed by an authorized officer
of the insurance company, showing that the insurance which Tenant is required to
maintain under this Section 4.04 is in full force and effect and containing such
other information which Landlord reasonably requires.

         (d) GENERAL INSURANCE PROVISIONS.

         (i) Any insurance which Tenant is required to maintain under this Lease
shall include a provision which requires the insurance carrier to give Landlord
not less than thirty (30) days written notice prior to any cancellation or
modification of such coverage.

         (ii) If Tenant falls to deliver any policy, certificate or renewal to
Landlord required under this Lease within the prescribed time period or if any
such policy is canceled or modified during the Lease Term without Landlord's
consent, Landlord may obtain such insurance, in which case Tenant shall
reimburse Landlord for the cost of such insurance within fifteen (15) days after
receipt of a statement that indicates the cost of such insurance. (See Exhibit D
for additional provisions, Tenant must maintain Environmental Policy for 2-years
beyond lease term)

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         (iii) Tenant shall maintain all insurance required under this Lease
with companies holding a "General Policy Rating" of A-12 or better, as set forth
in the most current Issue of "Best Key Rating Guide." Landlord and Tenant
acknowledge the insurance markets are rapidly changing and that insurance in the
form and amounts described in this Section 4.04 may not be available in the
future. Tenant acknowledges that the insurance described in this Section 4.04 is
for the primary benefit of Landlord. If at any time during the Lease Term,
Tenant is unable to maintain the insurance required under the Lease, Tenant
shall nevertheless maintain insurance coverage which is customary and
commercially reasonable in the insurance industry for Tenant's type of business,
as that coverage may change from time. Landlord makes no representation as to
the adequacy of such insurance to protect Landlord's or Tenant's interests.
Therefore, Tenant shall obtain any such additional property or liability
insurance which Tenant deems necessary to protect Landlord and Tenant.

         (iv) Landlord and Tenant each hereby waive any and all rights of
recovery against the other, or against the officers, employees, agents or
representatives of the other, for loss of or damage to its property or the
property of others under its control, if such loss or damage is covered by any
insurance policy in force (whether or not described in this Lease) at the time
of such loss or damage. Upon obtaining the required policies of insurance,
Landlord and Tenant shall give notice to the insurance carriers of this mutual
waiver of subrogation and shall cause their respective insurance carriers to
issue appropriate waiver of subrogation rights endorsements.

         Section 4.05. COMMON AREAS; USE, MAINTENANCE AND COSTS.

         (a) COMMON AREAS. As used in this Lease, "Common Areas" shall mean all
areas within the Project which are available for the common use of tenants of
the Project and which are not leased or held for the exclusive use of Tenant or
other tenants, including, but not limited to, parking areas, driveways,
sidewalks, loading areas, access roads, corridors, landscaping and planted
areas. Landlord, from time to time, may change the size, location, nature and
use of any of the Common Areas, convert Common Areas into leasable areas,
construct additional parking facilities (including parking structures) in the
Common Areas, and increase or decrease Common Area land and/or facilities.
Tenant acknowledges that such activities may result in inconvenience to Tenant.
Such activities and changes are permitted if they do not materially affect
Tenant's use of the Property.

         (b) USE OF COMMON AREAS. Tenant shall have the nonexclusive right (in
common with other tenants and all others to whom Landlord has granted or may
grant such rights) to use the Common Areas for the purposes intended, subject to
such reasonable rules and regulations as Landlord may establish from time to
time. Tenant shall abide by such rules and regulations and shall use its best
effort to cause others who use the Common Areas with Tenant's express or implied
permission to abide by Landlord's rules and regulations. At any time, Landlord
may close any Common Areas to perform any acts in the Common Areas as, in
Landlord's judgment, are desirable to improve the Project so long as it does not
materially affect Tenant's business. Tenant shall not interfere with the rights
of Landlord, other tenants or any other person entitled to use the Common Areas.

         (c) SPECIFIC PROVISION RE: VEHICLE PARKING. Tenant shall be entitled to
use the number of vehicle parking spaces in the Project allocated to Tenant in
Section 1.11 of the Lease without paying any additional rent. Tenant's parking
shall not be reserved and shall be limited to vehicles no larger than standard
size automobiles or pickup utility vehicles. Tenant shall not cause large trucks
or other large vehicles to be parked within the Project or on the adjacent
public streets. Temporary parking of large delivery vehicles in the Project may
be permitted by the rules and regulations established by Landlord. Vehicles
shall be parked only in striped parking spaces and not in driveways, loading
areas or other locations not specifically designated for parking. Handicapped
spaces shall only be used by those legally permitted to use them. If Tenant
parks more vehicles in the parking area than the number set forth in Section
1.11 of this Lease, such conduct shall be a material breach of this Lease. In
addition to Landlord's other remedies under the Lease, Tenant shall pay a daily
charge determined by Landlord for each such additional vehicle. This provision
shall not constitute default unless Landlord has given tenant two written
notices by fax under this provision. Tenant shall have five (5) business days to
cure.

         (d) MAINTENANCE OF COMMON AREAS. Landlord shall maintain the Common
Areas in good order, condition and repair and shall operate the Project, in
Landlord's sole discretion, as a first-class industrial/commercial real property
development. Tenant shall pay Tenant's pro rata share (as determined below) of
all costs incurred by Landlord for the operation and maintenance of the Common
Areas. Common Area costs include, but are not limited to, costs and expenses for
the following: gardening and landscaping; utilities, water and sewage charges;
maintenance of signs (other than tenants' signs); premiums for liability,
property damage, fire and other types of casualty insurance on the Common Areas
and worker's compensation insurance; all property taxes and assessments levied
on or attributable to the Common Areas and all Common Area improvements; all
personal property taxes levied on or attributable to personal property used in
connection with the Common Areas; straight-line depreciation on personal
property owned by Landlord which is consumed in the operation or maintenance of
the Common Areas; rental or lease payments paid by Landlord for rented or leased
personal property used in the operation or maintenance of the Common Areas; fees
for required licenses and permits; repairing, resurfacing, repaving,
maintaining, painting, lighting, cleaning, refuse removal, security and similar
items; reasonable reserves for roof replacement and exterior painting and other
appropriate reserves; and a reasonable allowance to Landlord for Landlord's
supervision of the Common Areas (management fee) (not to exceed five percent
(5%) of the gross rents of the Project for the calendar year). Landlord may
cause any or all of such services to be provided by third parties and the cost
of such services shall be included in Common Area costs. Common Area costs shall
not include depreciation of real property which forms part of the Common Areas,
or capitol expenditures. Landlord will not double charge on any repair or
replace expenses. Reserves are established for major replacement items, not for
repair items.

         (e) TENANT'S SHARE AND PAYMENT. Tenant shall pay Tenant's annual pro
rata share of all Common Area costs (prorated for any fractional month) upon
written notice from Landlord that such costs are due and payable, and in any
event prior to delinquency. Tenant's pro rata share shall be calculated by
dividing the square foot area of the Property, as set forth in Section 1.04 of
the Lease, by the aggregate square foot area of the Project which is leased or
held for lease by tenants, as of the date

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on which the computation is made. Tenant's initial pro rata share Is set out in
Paragraph 1.12(b). Any changes in the Common Area costs and/or the aggregate
area of the Project leased or held for lease during the Lease Term shall be
effective on the first day of the month after such change occurs. Landlord may,
at Landlord's election, estimate in advance and charge to Tenant as Common Area
costs, all real property taxes for which Tenant is liable under Section 4.02 of
the Lease, all insurance premiums for which Tenant is liable under Section 4.04
of the Lease, all maintenance and repair costs for which Tenant is liable under
Section 6.04 of the Lease, and all other Common Area costs payable by Tenant
hereunder. At Landlord's election, such statements of estimated Common Area
costs shall be delivered monthly, quarterly or at any other periodic intervals
to be designated by Landlord. Landlord may adjust such estimates at any time
based upon Landlord's experience and reasonable anticipation of costs, but not
more than once per year. Such adjustments shall be effective as of the next rent
payment date after notice to Tenant. Tenant shall have the ability to audit
these expenses two times per year. Landlord shall make available all of these
expense items for Tenant's review. Within sixty (60) days after the end of each
calendar year of the Lease Term, Landlord shall deliver to Tenant a statement
prepared in accordance with generally accepted accounting principles setting
forth, in reasonable detail, the Common Area costs paid or incurred by Landlord
during the preceding calendar year and Tenant's pro rata share. Upon receipt of
such statement, there shall be an adjustment between Landlord and Tenant, with
payment to or credit given by Landlord (as the case may be) so that Landlord
shall receive the entire amount of Tenant's share of such costs and expenses for
such period.

         Section 4.06. LATE CHARGES. Tenant's failure to pay rent promptly may
pause Landlord to incur unanticipated costs. The exact amount of such costs are
impractical or extremely difficult to ascertain. Such costs may include, but are
not limited to, processing and accounting charges and late charges which may be
imposed on Landlord by any ground lease, mortgage or trust deed encumbering the
Property. Therefore, if Landlord does not receive any rent payment within ten
(10) days after it becomes due, Tenant shall pay Landlord a late charge equal to
ten percent (10%) of the overdue amount. The parties agree that such late charge
represents a fair and reasonable estimate of the costs Landlord will incur by
reason of such late payment.

         Section 4.07. INTEREST ON PAST DUE OBLIGATIONS. Any amount owed by
Tenant to Landlord which is not paid when due shall bear interest at the rate of
fifteen percent (15%) per annum from the due date of such amount. However,
interest shall not be payable on late charges to be paid by Tenant under this
Lease. The payment of interest on such amounts shall not excuse or cure any
default by Tenant under this Lease. If the interest rate specified in this Lease
is higher than the rate permitted by law, the interest rate is hereby decreased
to the maximum legal interest rate permitted by law. Tenant shall have a ten
(10) day grace period on past due obligations.

         Section 4.08. IMPOUNDS FOR INSURANCE PREMIUMS AND REAL PROPERTY TAXES.
If requested by any ground lessor or lender to whom Landlord has granted a
security interest in the Property, or if Tenant is more than ten (10 ) days late
in the payment of rent more than once in any consecutive twelve (12) -month
period, Tenant shall pay Landlord a sum equal to one-twelfth (1/12) of the
annual real property taxes and insurance premiums payable by Tenant under this
Lease, together with each payment of Base Rent. Landlord shall hold such
payments in a non-interest bearing impound account. If unknown, Landlord shall
reasonably estimate the amount of real property taxes and insurance premiums
when due. Tenant shall pay any deficiency of funds in the impound account to
Landlord upon written request and Landlord shall pay any excess of funds in the
impound account to the Tenant. If Tenant defaults under this Lease, Landlord may
apply any funds in the impound account to any obligation then due under this
Lease.

ARTICLE 5 USE OF PROPERTY

         Section 5.01. PERMITTED USES. Tenant may use the Property only for the
Permitted Uses set forth in Section 1.06 above.

         Section 5.02. MANNER OF USE. Tenant shall not cause or permit the
Property to be used in any way which constitutes a violation of any law,
ordinance, or governmental regulation or order, which annoys or interferes with
the rights of tenants of the Project, or which constitutes a nuisance or waste.
Tenant shall obtain and pay for all permits, including a Certificate of
Occupancy, required for Tenant's occupancy of the Property and shall promptly
take all actions necessary to comply with all applicable statutes, ordinances,
rules, regulations, orders and requirements regulating the use by Tenant of the
Property, including the Occupational Safety and Health Act. Landlord shall pay
for all permits and fees in preparing space for Tenant's occupancy. These
amounts are included in Tenant's finish allowance.

         Section 5.03. HAZARDOUS MATERIALS. As used in this Lease, the term
"Hazardous Material" means any flammable items, explosives, radioactive
materials, hazardous or toxic substances, material or waste or related
materials, including any substances defined as or included in the definition of
"hazardous substances", "hazardous wastes", "hazardous materials" or "toxic
substances" now or subsequently regulated under any applicable federal, state or
local laws or regulations, including without limitation petroleum-based
products, paints, solvents, lead, cyanide, DDT, printing inks, acids,
pesticides, ammonia compounds and other chemical products, asbestos, PCBs and
similar compounds, and including any different products and materials which are
subsequently found to have adverse effects on the environment or the health and
safety of persons. Tenant shall not cause or permit any Hazardous Material to be
generated, produced, brought upon, used, stored, treated or disposed of in or
about the Property by Tenant, its agents, employees, contractors, sublessees or
invitees without the prior written consent of Landlord. Landlord shall be
entitled to take into account such other factors or facts as Landlord may
reasonably determine to be relevant in determining whether to grant or withhold
consent to Tenant's proposed activity with respect to Hazardous Material. In no
event, however, shall Landlord be required to consent to the installation or use
of any storage tanks on the Property. See Exhibit D for additional provisions
regarding the use of Radioactive Materials in the 8,540 SF lab area.

         Section 5.04. SIGNS AND AUCTIONS. Tenant shall not place any signs on
the Property without Landlord's prior written consent. Tenant shall not conduct
or permit any auctions or sheriff's sales at the Property.

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         Section 5.05. INDEMNITY. Tenant shall indemnify Landlord against and
hold Landlord harmless from any and all costs, claims or liability arising from:
(a) Tenant's use of the Property; (b) the conduct of Tenant's business or
anything else done or permitted by Tenant to be done in or about the Property,
including any contamination of the Property or any other property resulting from
the presence or use of Hazardous Material caused or permitted by Tenant; (c) any
breach or default in the performance of Tenant's obligations under this Lease;
(d) any misrepresentation or breach of warranty by Tenant under this Lease; or
(e) other acts or omissions of Tenant. Tenant shall defend Landlord against any
such cost, claim or liability at Tenant's expense with counsel reasonably
acceptable to Landlord, or, at Landlord's election, Tenant shall reimburse
Landlord for any reasonable legal fees or costs Incurred by Landlord in
connection with any such claim. As a material part of the consideration to
Landlord, Tenant assumes all risk of damage to property or injury to persons in
or about the Property arising from any cause, and Tenant hereby waives all
claims in respect thereof against Landlord, except for any claim arising out of
Landlord's gross negligence or willful misconduct. As used in this Section, the
term "Tenant" shall include Tenant's employees, agents, contractors and
invitees, if applicable.

         Section 5.06. LANDLORD'S ACCESS. Landlord or its agents may enter the
Property at all reasonable times to show the Property to potential buyers,
investors or tenants or other parties; to do any other act or to inspect and
conduct tests in order to monitor Tenant's compliance with all applicable
environmental laws and all laws governing the presence and use of Hazardous
Material; or for any other purpose Landlord deems necessary. Landlord shall give
Tenant prior notice of such entry, except in the case of an emergency. Landlord
may place customary "For Sale" or "For Lease" signs on the Property during the
last six (6) months of the lease term.

         Section 5.07. QUIET POSSESSION. If Tenant pays the rent and complies
with all other terms of this Lease, Tenant may occupy and enjoy the Property for
the full Lease Term, subject to the provisions of this Lease.

ARTICLE 6 CONDITION OF PROPERTY: MAINTENANCE, REPAIRS AND ALTERATIONS

         Section 6.01. EXISTING CONDITIONS. Tenant accepts the Property in its
condition as of the execution of the Lease, subject to all recorded matters,
laws, ordinances, and governmental regulations and orders. Except as provided
herein, Tenant acknowledges that neither Landlord nor any agent of Landlord has
made any representation as to the condition of the Property or the suitability
of the Property for Tenant's intended use. Tenant represents and warrants that
Tenant has made its own inspection of and inquiry regarding the condition of the
Property and is not relying on any representations of Landlord or any Broker
with respect thereto.

         Section 6.02. EXEMPTION OF LANDLORD FROM LIABILITY. Landlord shall not
be liable for any damage or business (or any loss of income therefrom), goods,
wares, merchandise or other property of Tenant, Tenant's employees, invitees,
customers or any other person in or about the Property, whether such damage or
injury is caused by or results from: (a) fire, steam, electricity, water, gas or
rain; (b) the breakage, leakage, obstruction or other defects of pipes,
sprinklers, wires, appliances, plumbing, air conditioning or lighting fixtures
or any other cause; (c) conditions arising in or about the Property or upon
other portions of the Project, or from other sources or places; or (d) any act
or omission of any other tenant of the Project. Landlord shall not be liable for
any such damage or injury even though the cause of or the means of repairing
such damage or injury are not accessible to Tenant. The provisions of this
Section 6.02 shall not, however, exempt Landlord from liability for Landlord's
negligence or willful misconduct.

         Section 6.03. LANDLORD'S OBLIGATIONS.

         (a) Except as provided in Article Seven (Damage or Destruction) and
Article Eight (Condemnation), Landlord shall keep the following in good order,
condition and repair: the foundations, exterior walls and roof of the Property
(including painting the exterior surface of the exterior walls of the Property
not more often than once very five (5) years, if necessary) and all components
of electrical, mechanical, plumbing, heating and air conditioning systems and
facilities located in the Property which are concealed or used in common by
tenants of the Project. However, Landlord shall not be obligated to maintain or
repair windows, doors, plate glass or the interior surfaces of exterior walls.
Landlord shall make repairs under this Section 6.03 within a reasonable time
after receipt of written notice from Tenant of the need for such repairs.

         (b) Tenant shall pay or reimburse Landlord for all costs Landlord
incurs under Paragraph 6.03(a) above as Common Area costs less any original
construction warranties as provided for in Section 4.05 of the Lease. Tenant
waives the benefit of any statute in effect now or in the future which might
give Tenant the right to make repairs at Landlord's expense or to terminate this
Lease due to Landlord's failure to keep the Property in good order, condition
and repair.

         Section 6.04. TENANT'S OBLIGATIONS.

         (a) Except as provided in Section 6.03, Article Seven (Damage or
Destruction) and Article Eight (Condemnation), Tenant shall keep all portions of
the Property (including structural, nonstructural, interior, systems and
equipment) in good order, condition and repair (including interior repainting
and refinishing, as needed). If any portion of the Property or any system or
equipment in the Property which Tenant is obligated to repair cannot be fully
repaired or restored, Tenant shall promptly replace such portion of the Property
or system or equipment in the Property, regardless of whether the benefit of
such replacement extends beyond the Lease Term; but if the benefit or useful
life of such replacement extends beyond the Lease Term (as such term may be
extended by exercise of any options), the useful life of such replacement shall
be prorated over the remaining portion of the Lease Term (as extended), and
Tenant shall be liable only for that portion of the cost which is applicable to
the Lease Term (as extended). Landlord shall maintain and Tenant shall pay for a
separate a preventive maintenance contract providing for the regular inspection
and maintenance of the heating and air conditioning system by a licensed heating
and air conditioning contractor. If any part of the Property or the Project is
damaged by any act or omission of Tenant and not covered by Insurance, Tenant
shall pay Landlord the cost of repairing or replacing such damaged property,
whether or not Landlord would otherwise be obligated to pay the cost of
maintaining or repairing such property. It is the

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intention of Landlord and Tenant that at all times Tenant shall maintain the
portions of the Property which Tenant is obligated to maintain in an attractive,
first-class and fully operative condition.

         (b) Tenant shall fulfill all of Tenant's obligations under this Section
6.04 at Tenant's sole expense. If Tenant fails to maintain, repair or replace
the Property as required by this Section 6.04, Landlord may, upon ten (10) days'
prior notice to Tenant (except that no notice shall be required in the case of
an emergency), enter the Property and perform such maintenance or repair
(including replacement, as needed) on behalf of Tenant. In such case, Tenant
shall reimburse Landlord for all reasonable costs incurred in performing such
maintenance or repair immediately upon demand.

         Section 6.05. ALTERATIONS, ADDITIONS, AND IMPROVEMENTS.

         (a) Tenant shall not make any alterations, additions, or improvements
to the Property without Landlord's prior written consent which consent shall not
be unreasonably withheld, except for non-structural alterations which do not
exceed Ten Thousand Dollars ($10,000) in cost cumulatively over the Lease Term
and which are not visible from the outside of any building of which the Property
is part. Landlord shall review and notify Tenant of acceptance or desired
modification with five (5) business days. Landlord may require Tenant to provide
demolition and/or lien and completion bonds in form and amount satisfactory to
Landlord. Tenant shall promptly remove any alterations, additions, or
improvements constructed in violation of this Paragraph 6.05(a) upon Landlord's
written request. All alterations, additions, and improvements shall be done in a
good and workmanlike manner, in conformity with all applicable laws and
regulations, and by a contractor approved by Landlord which approval shall not
be unreasonably withheld. Upon completion of any such work, Tenant shall provide
Landlord with "as built" plans, copies of all construction contracts, and proof
of payment for all labor and materials.

         (b) Tenant shall pay when due all claims for labor and material
furnished to the Property. Tenant shall give Landlord at least twenty (20) days'
prior written notice of the commencement of any work on the Property, regardless
of whether Landlord's consent to such work is required. Landlord may elect to
record and post notices of non-responsibility on the Property.

         Section 6.06. CONDITION UPON TERMINATION. Upon the termination of the
Lease, Tenant shall surrender the Property to Landlord, broom clean and in the
same condition as received except for ordinary wear and tear which Tenant was
not otherwise obligated to remedy under any provision of this Lease. However,
Tenant shall not be obligated to repair any damage which Landlord is required to
repair under Article Seven (Damage or Destruction). In addition, Landlord may
require Tenant to remove any alterations, additions or improvements (whether or
not made with Landlord's consent) prior to the expiration of the Lease and to
restore the Property to its prior condition, all at Tenant's expense; provided,
however, in no event shall Tenant be required to remove any alterations to the
Property that are made prior to April 15, 2002. All alterations, additions and
improvements which Landlord has not required Tenant to remove shall become
Landlord's property and shall be surrendered to Landlord upon the expiration or
earlier termination of the Lease, except that Tenant may remove any of Tenant's
machinery or equipment which can be removed without material damage to the
Property. Tenant shall repair, at Tenant's expense, any damage to the Property
caused by the removal of any such machinery or equipment. In no event, however,
shall Tenant remove any of the following materials or equipment (which shall be
deemed Landlord's property) without Landlord's prior written consent: any power
wiring or power panels; lighting or lighting fixtures; wall coverings; drapes,
blinds or other window coverings; carpets or other floor coverings; heaters, air
conditioners or any other heating or air conditioning equipment; fencing or
security gates; or other similar building operating equipment and decorations.
Notwithstanding the foregoing, Tenant may remove any of its furniture, trade
fixtures or equipment at the end of the term or upon the earlier termination of
this Lease, to the extent that such furniture, trade fixtures or equipment have
not been built-in to the Property and can be readily removed without permanent
damage to the Property.

ARTICLE 7 DAMAGE OR DESTRUCTION

         Section 7.01. PARTIAL DAMAGE TO PROPERTY.

         (a) Tenant shall notify Landlord in writing immediately upon the
occurrence of any damage to the Property. If the Property is only partially
damaged (i.e., less than fifty percent (50%) of the Property is untenantable as
a result of such damage or less than fifty percent (50%) of Tenant's operations
are materially impaired) and if the proceeds received by Landlord from the
insurance policies described in Paragraph 4.04(b) are sufficient to pay for the
necessary repairs, this Lease shall remain in effect and Landlord shall repair
the damage as soon as reasonably possible such repairs to be completed within
one hundred eighty (180) business days failing which Tenant may terminate this
lease. Landlord may elect (but is not required) to repair any damage to Tenant's
fixtures, equipment, or improvements.

         (b) If the insurance proceeds received by Landlord are not sufficient
to pay the entire cost of repair, or if the cause of the damage is not covered
by the insurance policies which Landlord maintains under Paragraph 4.04(b),
Landlord may elect either to (i) repair the damage as soon as reasonably
possible, in which case this Lease shall remain in full force and effect, or
(ii) terminate this Lease as of the date the damage occurred. Landlord shall
notify Tenant within thirty (30) days after receipt of notice of the occurrence
of the damage whether Landlord elects to repair the damage or terminate the
Lease. If Landlord elects to repair the damage, Tenant shall pay Landlord its
pro-rata share of the "deductible amount" (if any) under Landlord's insurance
policies and, if the damage was due to an act or omission of Tenant, or Tenant's
employees, agents, contractors or invitees, the difference between the actual
cost of repair and any insurance proceeds received by Landlord. If Landlord
elects to terminate the Lease, Tenant may elect to continue this Lease in full
force and effect, in which case Tenant shall repair any damage to the Property
and any building in which the Property is located. Tenant shall pay the cost of
such repairs, except that upon satisfactory completion of such repairs, Landlord
shall deliver to Tenant any such insurance proceeds received by Landlord for the
damage repaired by Tenant. Tenant shall give Landlord written notice of such
election within ten (10) days after receiving Landlord's termination notice.

         (c) If the damage to the Property occurs during the last six (6) months
of the Lease Term and such damage will require more than thirty (30) days to
repair, either Landlord or Tenant may elect to terminate this Lease as of the
date the damage

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occurred, regardless of the sufficiency of any insurance proceeds. The party
electing to terminate this Lease shall give written notification to the other
party of such election within thirty (30) days after Tenant's notice to Landlord
of the occurrence of the damage.

         Section 7.02. SUBSTANTIAL OR TOTAL DESTRUCTION. If the Property is
substantially or totally destroyed by any cause whatsoever (i.e., the damage to
the Property is greater than partial damage as described In Section 7.01), and
regardless of whether Landlord receives any insurance proceeds, this Lease shall
terminate as of the date the destruction occurred. Notwithstanding the preceding
sentence, if the Property can be rebuilt within six (6) months after the date of
destruction, Landlord may elect to rebuild the Property at Landlord's own
expense, in which case this Lease shall remain in full force and effect, so long
as Landlord provides to Tenant, on a rent-free basis, temporary substitute space
at the Project that is reasonably acceptable to Tenant and is adequate to enable
Tenant to continue to carry on its business, during the repair and rebuilding
period. Landlord shall notify Tenant of such election within thirty (30) days
after Tenant's notice of the occurrence of total or substantial destruction. If
Landlord so elects, Landlord shall rebuild the Property at Landlord's sole
expense, except that if the destruction was caused by an act or omission of
Tenant, Tenant shall pay Landlord the difference between the actual cost of
rebuilding and any insurance proceeds received by Landlord.

         Section 7.03. TEMPORARY REDUCTION OF RENT. If the Property is destroyed
or damaged and Landlord or Tenant repairs or restores the Property pursuant to
the provisions of this Article Seven, any rent payable during the period of such
damage, repair and/or restoration shall be reduced according to the degree, if
any, to which Tenant's use of the Property is impaired. Except for such possible
reduction in Rent, Tenant shall not be entitled to any compensation, reduction,
or reimbursement from Landlord as a result of any damage, destruction, repair,
or restoration of or to the Property.

         Section 7.04. WAIVER. Tenant waives the protection of any statute, code
or judicial decision which grants a tenant the right to terminate a lease in the
event of the substantial or total destruction of the leased property. Tenant
agrees that the provisions of Section 7.02 above shall govern the rights and
obligations of Landlord and Tenant in the event of any substantial or total
destruction to the Property.

ARTICLE 8 CONDEMNATION

         If all or any portion of the Property is taken under the power of
eminent domain or sold under the threat of that power (all of which are called
"Condemnation"), this Lease shall terminate as to the part taken or sold on the
date the condemning authority takes title or possession, whichever occurs first.
If more than twenty percent (20%) of the floor area of the building in which the
Property is located, or which is located on the Property, is taken, either
Landlord or Tenant may terminate this Lease as of the date the condemning
authority takes title or possession, by delivering written notice to the other
within ten (110) days after receipt of written notice of such taking (or in the
absence of such notice, within ten (110) days after the condemning authority
takes title or possession). If neither Landlord nor Tenant terminates this
Lease, this Lease shall remain in effect as to the portion of the Property not
taken, except that the Base Rent and Additional Rent shall be reduced in
proportion to the reduction in the floor area of the Property. Any Condemnation
award or payment shall be distributed in the following order: (a) first, to any
ground lessor, mortgagee or beneficiary under a deed of trust encumbering the
Property, the amount of its interest in the Property; (b) second, to Tenant,
only the amount of any award specifically designated for loss of or damage to
Tenant's trade fixtures or removable personal property; and (c) third, to
Landlord, the remainder of such award, whether as compensation for reduction in
the value of the leasehold, the taking of the fee, or otherwise. If this Lease
is not terminated, Landlord shall repair any damage to the Property caused by
the Condemnation, except that Landlord shall not be obligated to repair any
damage for which Tenant has been reimbursed by the condemning authority. If the
severance damages received by Landlord are not sufficient to pay for such
repair, Landlord shall have the right to either terminate this Lease or make
such repair at Landlord's expense.

ARTICLE 9 ASSIGNMENT AND SUBLETTING

         Section 9.01. LANDLORD'S CONSENT REQUIRED. No portion of the Property
or of Tenant's interest in this Lease may be acquired by any other person or
entity, whether by sale, assignment, mortgage, sublease, transfer, operation of
law, or act of Tenant, without Landlord's prior written consent, except as
provided in Section 9.02 below. Landlord has the right to grant or withhold its
consent as provided in Section 9.05 below. Any attempted transfer without
consent shall be void and shall constitute a non-curable breach of this Lease.
If Tenant is a partnership, any cumulative transfer of more than twenty percent
(20%) of the partnership interests shall require Landlord's consent. If Tenant
is a corporation, any change in the ownership of more than 50% of the
outstanding shares of the corporation shall require Landlord's consent, such
consent not to be unreasonably withheld.

         Section 9.02. TENANT AFFILIATE. Tenant may assign this Lease or
sublease the Property, without Landlord's consent, to any corporation which
controls, is controlled by or is under common control with Tenant, or to any
entity resulting from the merger of or consolidation with Tenant or the
purchaser of all or substantially all the assets of Tenant ("Tenant's
Affiliate"). In such case, any Tenant's Affiliate shall assume in writing all of
Tenant's obligations under this Lease.

         Section 9.03. NO RELEASE OF TENANT. No transfer permitted by this
Article Nine, whether with or without Landlord's consent, shall release Tenant
or change Tenant's primary liability to pay the rent and to perform all other
obligations of Tenant under this Lease. Landlord's acceptance of rent from any
other person Is not a waiver of any provision of this Article Nine. Consent to
one transfer is not a consent to any subsequent transfer. If Tenant's transferee
defaults under this Lease, Landlord may proceed directly against Tenant without
pursuing remedies against the transferee. Landlord may consent to subsequent
assignments or modifications of this Lease by Tenant's transferee, without
notifying Tenant or obtaining its consent. Such action shall not relieve
Tenant's liability under this Lease.

         Section 9.04. OFFER TO TERMINATE. If Tenant desires to assign the Lease
or sublease the Property TO ANYONE OTHER THAN TENANT'S AFFILIATE, Tenant shall
have the right to offer, in writing, to terminate the Lease as of a date
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Landlord elects in writing to accept the offer to terminate within twenty (20)
days after notice of the offer, the Lease shall terminate as of the date
specified and all the terms and provisions of the Lease governing termination
shall apply. If Landlord does not so elect, the Lease shall continue in effect
until otherwise terminated and the provisions of Section 9.05 with respect to
any proposed transfer shall continue to apply.

         Section 9.05. LANDLORD'S CONSENT.

         (a) Tenant's request for consent to any transfer described in Section
9.01 shall set forth in writing the details of the proposed transfer, including
the name, business and financial condition of the prospective transferee,
financial details of the proposed transfer (e.g., the term of and the rent and
security deposit payable under any proposed assignment or sublease), and any
other information Landlord deems relevant. Landlord shall have the right to
withhold consent, if reasonable, or to grant consent, based on the following
factors: (i) the business of the proposed assignee or subtenant and the proposed
use of the Property; (ii) the net worth and financial reputation of the proposed
assignee or subtenant; (iii) Tenant's compliance with all of its obligations
under the Lease; and (iv) such other factors as Landlord may reasonably deem
relevant. If Landlord objects to a proposed assignment solely because of the net
worth and/or financial reputation of the proposed assignee, Tenant may
nonetheless sublease (but not assign), all or a portion of the Property to the
proposed transferee, but only on the other terms of the proposed transfer.

         (b) If Tenant assigns or subleases, the following shall apply:

         (i) Tenant shall pay to Landlord as Additional Rent under the Lease the
Landlord's Share (stated in Section 1.13) of the Profit (defined below) on such
transaction as and when received by Tenant, unless Landlord gives written notice
to Tenant and the assignee or subtenant that Landlord's Share shall be paid by
the assignee or subtenant to Landlord directly. The "Profit" means (A) all
amounts paid to Tenant for such assignment or sublease, including "key" money,
monthly rent in excess of the monthly rent payable under the Lease, and all fees
and other consideration paid for the assignment or sublease, including fees
under any collateral agreements, less (B) costs and expenses directly incurred
by Tenant in connection with the execution and performance of such assignment or
sublease for real estate broker's commissions and costs of renovation or
construction of tenant improvements required under such assignment or sublease.
Tenant Is entitled to recover such costs and expenses before Tenant Is obligated
to pay the Landlord's Share to Landlord. The Profit in the case of a sublease of
less than all the Property is the rent allocable to the subleased space as a
percentage on a square footage basis.

         (ii) Tenant shall provide Landlord a written statement certifying all
amounts to be paid from any assignment or sublease of the Property within thirty
(30) days after the transaction documentation is signed, and Landlord may
inspect Tenant's book and records to verify the accuracy of such statement. On
written request, Tenant shall promptly furnish to Landlord copies of all the
transaction documentation, all of which shall be certified by Tenant to be
complete, true and correct. Landlord's receipt of Landlord's Share shall not be
a consent to any further assignment or subletting. The breach of Tenant's
obligation under this Paragraph 9.05(b) shall be a material default of the
Lease.

         Section 9.06. NO MERGER. No merger shall result from Tenant's sublease
of the Property under this Article Nine, Tenant's surrender of this Lease or the
termination of this Lease in any other manner. In any such event, Landlord may
terminate any or all subtenancies or succeed to the interest of Tenant as
sublandlord under any or all subtenancies.

ARTICLE 10 DEFAULTS; REMEDIES

         Section 10.01. COVENANTS AND CONDITIONS. Tenant's performance of each
of Tenant's obligations under this Lease is a condition as well as a covenant.
Tenant's right to continue in possession of the Property is conditioned upon
such performance. Time is of the essence in the performance of all covenants and
conditions. Tenant shall abide by the Church Ranch Home Place Protective
Covenants as well as the Rules and Regulations for the Church Ranch Business
Center.

         Section 10.02. DEFAULTS. Tenant shall be in material default under this
Lease:

         (a) If Tenant abandons the Property or if Tenant's vacation of the
Property results in the cancellation of any insurance described in Section 4.04;

         (b) It Tenant fails to pay rent or any other charge when due, and such
default continues for five business days after written notice from Landlord;
however, Tenant will not be entitled to more than two written notices for
monetary defaults during any 12-month period, and if after two such written
notices any rent is not paid when due, a default will be considered to have
occurred without further notice;

         (c) If Tenant fails to perform any of Tenant's non-monetary obligations
under this Lease for a period of thirty (30) days after written notice from
Landlord; provided that if more than thirty (30) days are required to complete
such performance, Tenant shall not be in default if Tenant commences such
performance within the thirty (30) -day period and thereafter diligently pursues
its completion. However, Landlord shall not be required to give such notice if
Tenant's failure to perform constitutes a non-curable breach of this Lease. The
notice required by this Paragraph is intended to satisfy any and all notice
requirements imposed by law on Landlord and is not in addition to any such
requirement.

         (d) (i) If Tenant makes a general assignment or general arrangement for
the benefit of creditors; (ii) if a petition for adjudication of bankruptcy or
for reorganization or rearrangement is filed by or against Tenant and is not
dismissed within thirty (30) days; (iii) if a trustee or receiver is appointed
to take possession of substantially all of Tenant's assets located at the
Property or of Tenant's interest in this Lease and possession is not restored to
Tenant within thirty (30) days; or (iv) if substantially all of Tenant's assets
located at the Property or of Tenant's interest in this Lease is subjected to
attachment, execution or other judicial seizure which is not discharged within
thirty (30) days. If a court of competent jurisdiction determines that any of
the acts described in this subparagraph (d) is not a default under this Lease,
and a trustee is appointed to take possession (or if Tenant remains a debtor in
possession) and such trustee or Tenant transfers Tenant's interest hereunder,

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then Landlord shall receive, as Additional Rent, the excess, if any, of the rent
(or any other consideration) paid in connection with such assignment or sublease
over the rent payable by Tenant under this Lease.

         (e) If any guarantor of the Lease revokes or otherwise terminates, or
purports to revoke or otherwise terminate, any guaranty of all or any portion of
Tenant's obligations under the Lease. Unless otherwise expressly provided, no
guaranty of the Lease is revocable.

         Section 10.03. REMEDIES. On the occurrence of any material default by
Tenant, Landlord may, at any time thereafter, with or without notice or demand
and without limiting Landlord in the exercise of any right or remedy which
Landlord may have:

         (a) Terminate Tenant's right to possession of the Property by any
lawful means, in which case this Lease shall terminate and Tenant shall
immediately surrender possession of the Property to Landlord. In such event,
Landlord shall be entitled to recover from Tenant all damages incurred by
Landlord by reason of Tenant's default, including (i) the worth at the time of
the award of the unpaid Base Rent, Additional Rent and other charges which
Landlord had earned at the time of the termination; (ii) the worth at the time
of the award of the amount by which the unpaid Base Rent, additional Rent and
other charges which Landlord would have earned after termination until the time
of the award exceeds the amount of such rental loss that Tenant proves Landlord
could have reasonably avoided; (iii) the worth at the time of the award of the
amount by which the unpaid Base Rent, Additional Rent and other charges which
Tenant would have paid for the balance of the Lease Term after the time of award
exceeds the amount of such rental loss that Tenant proves Landlord could have
reasonably avoided; and (iv) any other amount necessary to compensate Landlord
for all the detriment proximately caused by Tenant's failure to perform its
obligations under the Lease or which in the ordinary course of things would be
likely to result therefrom, including, but not limited to, any costs or expenses
Landlord incurs in maintaining or preserving the Property after such default,
the cost of recovering possession of the Property, expenses of reletting,
including necessary renovation or alteration of the Property, Landlord's
reasonable attorneys' fees incurred in connection therewith, and any real estate
commission paid or payable. As used in subparts (i) and (ii) above, the "worth
at the time of the award" is computed by allowing interest on unpaid amounts at
the rate of fifteen percent (15%) per annum, or such lesser amount as may then
be the maximum lawful rate. As used in subpart (iii) above, the "worth at the
time of the award" Is computed by discounting such amount at the discount rate
of the Federal Reserve Bank of San Francisco at the time of the award, plus one
percent (1%). If Tenant has abandoned the Property, Landlord shall have the
option of (i) retaking possession of the Property and recovering from Tenant the
amount specified in this Paragraph 10.03(a), or (ii) proceeding under Paragraph
10.03(b);

         (b) Maintain Tenant's right to possession, in which case this Lease
shall continue in effect whether or not Tenant has abandoned the Property. In
such event, Landlord shall be entitled to enforce all of Landlord's rights and
remedies under this Lease, including the right to recover the rent as it becomes
due;

         (c) Pursue any other remedy now or hereafter available to Landlord
under the laws or judicial decisions of the state in which the Property is
located.

         Section 10.04. REPAYMENT OF "FREE" RENT. If this Lease provides for a
postponement of any monthly rental payments, a period of "free" rent or other
rent concession, such postponed rent or "free" rent is called the "Abated Rent."
Tenant shall be credited with having paid all of the Abated Rent on the
expiration of the Lease Term only if Tenant has fully, faithfully, and
punctually performed all of Tenant's obligations hereunder, including the
payment of all rent (other than the Abated Rent) and all other monetary
obligations and the surrender of the Property in the physical condition required
by this Lease. Tenant acknowledges that its right to receive credit for the
Abated Rent is absolutely conditioned upon Tenant's full, faithful and punctual
performance of it obligations under this Lease. If Tenant defaults and does not
cure within any applicable grace period, the Abated Rent shall immediately
become due and payable in full and this Lease shall be enforced as if there were
no such rent abatement or other rent concession. In such case Abated Rent shall
be calculated based on the full initial rent payable under this Lease.

         Section 10.05. AUTOMATIC TERMINATION. Notwithstanding any other term or
provision hereof to the contrary, the Lease shall terminate on the occurrence of
any act which affirms the Landlord's intention to terminate the Lease as
provided in Section 10.03 hereof, including the filing of an unlawful detainer
action against Tenant. On such termination, Landlord's damages for default shall
include all costs and fees, including reasonable attorneys' fees that Landlord
incurs in connection with the filing, commencement, pursuing and/or defending of
any action in any bankruptcy court or other court with respect to the Lease; the
obtaining of relief from any stay in bankruptcy restraining any action to evict
Tenant; or the pursuing of any action with respect to Landlord's right to
possession of the Property. All such damages suffered (apart from Base Rent and
other rent payable hereunder) shall constitute pecuniary damages which must be
reimbursed to Landlord prior to assumption of the Lease by Tenant or any
successor to Tenant in any bankruptcy or other proceeding.

         Section 10.06. CUMULATIVE REMEDIES. Landlord's exercise of any right or
remedy shall not prevent it from exercising any other right or remedy.

ARTICLE 11 PROTECTION OF LENDERS

         Section 11.01. SUBORDINATION. Landlord shall have the right to
subordinate this Lease to any ground lease, deed of trust or mortgage
encumbering the Property, any advances made on the security thereof and any
renewals, modifications, consolidations, replacements or extensions thereof,
whenever made or recorded. Tenant shall cooperate with Landlord and any lender
which is acquiring a security Interest in the Property or the Lease. Tenant
shall execute such further documents and assurances as such lender may require,
provided that Tenant's obligations under this Lease shall not be increased in
any material way (the performance of ministerial acts shall not be deemed
material), and Tenant shall not be deprived of its rights under this Lease.
Tenant's right to quiet possession of the Property during the Lease Term shall
not be disturbed if Tenant pays the rent and performs all of Tenant's
obligations under this Lease and is not otherwise in default. If any ground
lessor, beneficiary or mortgagee elects to have this Lease prior to the lien of
its ground lease, deed of trust or mortgage and gives

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written notice thereof to Tenant, this Lease shall be deemed prior to such
ground lease, deed of trust or mortgage whether this Lease is dated prior or
subsequent to the date of said ground lease, deed of trust or mortgage or the
date of recording thereof.

         Section 11.02. ATTORNMENT. If Landlord's interest in the Property is
acquired by any ground lessor, beneficiary under a deed of trust, mortgagee, or
purchaser at a foreclosure sale, Tenant shall attorn to the transferee of or
successor to Landlord's interest in the Property and recognize such transferee
or successor as Landlord under this Lease; provided, however, such transferee or
successor agrees that Tenant's rights in the Property shall not be disturbed so
long as Tenant is riot in default beyond applicable notice and cure periods
under the Lease, and has paid all amounts then owing. Tenant waives the
protection of any statute or rule of law which gives or purports to give Tenant
any right to terminate this Lease or surrender possession of the Property upon
the transfer of Landlord's interest.

         Section 11.03. SIGNING OF DOCUMENTS. Tenant shall sign and deliver any
instrument or documents necessary or appropriate to evidence any such attornment
or subordination or agreement to do so. If Tenant falls to do so within ten (10)
days after written request, Tenant hereby makes, constitutes and irrevocably
appoints Landlord, or any transferee or successor of Landlord, the
attorney-in-fact of Tenant to execute and deliver any such instrument or
document.

         Section 11.04. ESTOPPEL CERTIFICATES.

         (a) Upon Landlord's written request, Tenant shall execute, acknowledge
and deliver to Landlord a written statement certifying: (i) that none of the
terms or provisions of this Lease have been changed (or if they have been
changed, stating how they have been changed); (ii) that this Lease has not been
canceled or terminated; (iii) the last date of payment of the Base Rent and
other charges and the time period covered by such payment; (iv) that Landlord is
not in default under this Lease (or, if Landlord is claimed to be in default,
stating why); and (v) such other representations or information with respect to
Tenant or the Lease as Landlord may reasonable request or which any prospective
purchaser or encumbrancer of the Property may require. Tenant shall deliver such
statement to Landlord within ten (10) days after Landlord's request. If Tenant
fails to deliver such notice, Landlord shall deliver a second notice to Tenant.
If Tenant does not deliver such statement within a second ten day period, that
will be a default by Tenant of this lease. Landlord may give any such statement
by Tenant to any prospective purchaser or encumbrancer of the Property. Such
purchaser or encumbrancer may rely conclusively upon such statement as true and
correct.

         (b) If Tenant does not deliver such statement to Landlord within such
ten (10) -day period, Landlord, and any prospective purchaser or encumbrancer,
may conclusively presume and rely upon the following facts: (i) that the terms
and provisions of this Lease have not been changed except as otherwise
represented by Landlord; (ii) that this Lease has not been canceled or
terminated except as otherwise represented by Landlord; (iii) that not more than
one month's Base Rent or other charges have been paid in advance; and (iv) that
Landlord is not in default under the Lease. In such event, Tenant shall be
estopped from denying the truth of such facts.

         Section 11.05. TENANT'S FINANCIAL CONDITION. Within ten (10) days after
written request from Landlord, Tenant shall deliver to Landlord such financial
statements as Landlord reasonably requires to verity the net worth of Tenant or
any assignee, subtenant, or guarantor of Tenant. In addition, Tenant shall
deliver to any lender designated by Landlord any financial statements required
by such lender to facilitate the financing or refinancing of the Property.
Tenant represents and warrants to Landlord that each such financial statement is
a true and accurate statement as of the date of such statement. All financial
statements shall be confidential and shall be used only for the purposes set
forth in this Lease.

ARTICLE 12 LEGAL COSTS

         Section 12.01. LEGAL PROCEEDINGS. If Tenant or Landlord shall be In
breach or default under this Lease beyond applicable notice and cure periods,
such party (the "Defaulting Party") shall reimburse the other party (the
"Nondefaulting Party") upon demand for any costs or expenses that the
Nondefaulting Party incurs in connection with any breach or default of the
Defaulting Party under this Lease, whether or not suit is commenced or judgment
entered. Such costs shall include legal fees and costs incurred for the
negotiation of a settlement, enforcement of rights or otherwise. Furthermore, if
any action for breach of or to enforce the provisions of this Lease is
commenced, the court in such action shall award to the party in whose favor a
judgment is entered, a reasonable sum as attorneys' fees and costs. The losing
party in such action shall pay such attorneys' fees and costs. Tenant shall also
indemnify Landlord against and hold Landlord harmless from all costs, expenses,
demands and liability Landlord may incur if Landlord becomes or is made a party
to any claim or action (a) Instituted by Tenant against any third party, or by
any third party against Tenant, or by or against any person holding any interest
under or using the Property by license of or agreement with Tenant; (b) for
foreclosure of any lien for labor or material furnished to or for Tenant or such
other person; (c) otherwise arising out of or resulting from any act or
transaction of Tenant or such other person; or (d) necessary to protect
Landlord's interest under this Lease in a bankruptcy proceeding, or other
proceeding under Title 11 of the United States Code, as amended. Tenant shall
defend Landlord against any such claim or action at Tenant's expense with
counsel reasonably acceptable to Landlord or, at Landlord's election, Tenant
shall reimburse Landlord for any reasonable legal fees or costs Landlord incurs
in any such claim or action.

         Section 12.02. LANDLORD'S CONSENT. Tenant shall pay Landlord's
reasonable attorneys' fees incurred in connection with Tenant's request for
Landlord's consent under Article Nine (Assignment and Subletting), or in
connection with any other act which Tenant proposes to do and which requires
Landlord's consent.

ARTICLE 13 MISCELLANEOUS PROVISIONS

         Section 13.01. NON-DISCRIMINATION. Tenant promises, and it is a
condition to the continuance of this Lease, that there will be no discrimination
against, or segregation of, any person or group of persons on the basis of race,
color, sex, creed, national origin or ancestry in the leasing, subleasing,
transferring, occupancy, tenure or use of the Property or any portion thereof.

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         Section 13.02. LANDLORD'S LIABILITY; CERTAIN DUTIES.

         (a) As used in this Lease, the term "Landlord" means only the current
owner or owners of the fee title to the Property or Project or the leasehold
estate under a ground lease of the Property or Project at the time in question.
Each Landlord is obligated to perform the obligations of Landlord under this
Lease only during the time such Landlord owns such interest or title. Any
Landlord who transfers its title or interest is relieved of all liability with
respect to the obligations of Landlord under this Lease to be performed on or
after the date of transfer. However, each Landlord shall deliver to its
transferee all funds that Tenant previously paid if such funds have not yet been
applied under the terms of this Lease.

         (b) Tenant shall give written notice of any failure by Landlord to
perform any of its obligations under this Lease to Landlord and to any ground
lessor, mortgagee or beneficiary under any deed of trust encumbering the
Property whose name and address have been furnished to Tenant in writing.
Landlord shall not be in default under this Lease unless Landlord (or such
ground lessor, mortgagee or beneficiary) fails to cure such non-performance
within thirty (30) days after receipt of Tenant's notice. However, if such
non-performance reasonably requires more than thirty (30) days to cure, Landlord
shall not be in default if such cure is commenced with In such thirty (30) -day
period and thereafter diligently pursued to completion.

         (c) Notwithstanding any term or provision herein to the contrary, the
liability of Landlord for the performance of its duties and obligations under
this Lease is limited to Landlord's interest in the Property and the Project,
and neither the Landlord nor its partners, shareholders, officers or other
principals shall have any personal liability under this Lease.

         Section 13.03. SEVERABILITY. A determination by a court of competent
jurisdiction that any provision of this Lease or any part thereof is illegal or
unenforceable shall not cancel or invalidate the remainder of such provision of
this Lease, which shall remain in full force and effect.

         Section 13.04. INTERPRETATION. The captions of the Articles or Sections
of this Lease are to assist the parties in reading this Lease and are not a part
of the terms or provisions of this Lease. Whenever required by the context of
this Lease, the singular shall include the plural and the plural shall include
the singular. The masculine, feminine and neuter genders shall each include the
other. In any provision relating to the conduct, acts or omissions of Tenant,
the term "Tenant" shall include Tenant's agents, employees, contractors,
invitees, successors or others using the Property with Tenant's expressed or
implied permission.

         Section 13.05. INCORPORATION OF PRIOR AGREEMENTS; MODIFICATIONS. This
Lease is the only agreement between the parties pertaining to the lease of the
Property and no other agreements are effective. All amendments to this Lease
shall be in writing and signed by all parties. Any other attempted amendment
shall be void.

         Section 13.06. NOTICES. All notices required or permitted under this
Lease shall be in writing and shall be personally delivered or sent by certified
mail, return receipt requested, postage prepaid. Notices to Tenant shall be
delivered to the address specified in Section 1.03 above, except that upon
Tenant's taking possession of the Property, the Property shall be Tenant's
address for notice purposes. Notices to Landlord shall be delivered to the
address specified in Section 1.02 above. All notices shall be effective upon
delivery. Either party may change its notice address upon written notice to the
other party.

         Section 13.07. WAIVERS. All waivers must be in writing and signed by
the waiving party. Landlord's failure to enforce any provision of this Lease or
its acceptance of rent shall not be a waiver and shall not prevent Landlord from
enforcing that provision or any other provision of this Lease in the future. No
statement on a payment check from Tenant or in a letter accompanying a payment
check shall be binding on Landlord. Landlord may, with or without notice to
Tenant, negotiate such check without being bound to the conditions of such
statement.

         Section 13.08. NO RECORDATION. Tenant shall not record this Lease
without prior written consent from Landlord. However, either Landlord or Tenant
may require that a "Short Form" memorandum of this Lease executed by both
parties be recorded. The party requiring such recording shall pay all transfer
taxes and recording fees.

         Section 13.09. BINDING EFFECT; CHOICE OF LAW. This Lease binds any
party who legally acquires any rights or interest in this Lease from Landlord or
Tenant. However, Landlord shall have no obligation to Tenant's successor unless
the rights or interests of Tenant's successor are acquired in accordance with
the terms of this Lease. The laws of the state in which the Property is located
shall govern this Lease.

         Section 13.10 CORPORATE AUTHORITY; PARTNERSHIP AUTHORITY. If Tenant Is
a corporation, each person signing this Lease on behalf of Tenant represents and
warrants that he has full authority to do so and that this Lease binds the
corporation. Within thirty (30) days after this Lease is signed, Tenant shall
deliver to Landlord a certified copy of a resolution of Tenant's Board of
Directors authorizing the execution of this Lease or other evidence of such
authority reasonably acceptable to Landlord. If Tenant is a partnership, each
person or entity signing this Lease for Tenant represents and warrants that he
or it is a general partner of the partnership, that he or it has full authority
to sign for the partnership and that this Lease binds the partnership and all
general partners of the partnership. Tenant shall give written notice to
Landlord of any general partner's withdrawal or addition. Within thirty (30)
days after this Lease is signed, Tenant shall deliver to Landlord a copy of
Tenant's recorded statement of partnership or certificate of limited
partnership.

         Section 13.11 JOINT AND SEVERAL LIABILITY. All parties signing this
Lease as Tenant shall be jointly and severally liable for all obligations of
Tenant.

         Section 13.12 FORCE MAJEURE. If Landlord cannot perform any of its
obligations due to events beyond Landlord's control, the time provided for
performing such obligations shall be extended by a period of time equal to the
duration of such events. Events beyond Landlord's control include, but are not
limited to, acts of God, war, civil commotion, labor disputes, strikes, fire,
flood or other casualty, shortages of labor or material, government regulation
or restriction and weather conditions.

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         Section 13.13 EXECUTION OF LEASE. This Lease may be executed in
counterparts and, when all counterpart documents are executed, the counterparts
shall constitute a single binding instrument. Landlord's delivery of this Lease
to Tenant shall not be deemed to be an offer to lease and shall not be binding
upon either party until executed and delivered by both parties.

         Section 13.14 SURVIVAL. All representations and warranties of Landlord
and Tenant shall survive the termination of this Lease.

ARTICLE 14 BROKERS

         Section 14.01. BROKER'S FEE. When this Lease is signed by and delivered
to both Landlord and Tenant, Landlord shall pay a real estate commission to
Landlord's Broker named in Section 1.08 above, if any, as provided in the
written agreement between Landlord and Landlord's Broker, or the sum stated in
Section 1.09 above for services rendered to Landlord by Landlord's Broker in
this transaction. Landlord shall pay Landlord's Broker a commission if Tenant
exercises any option to extend the Lease Term or to buy the Property, or any
similar option or right which Landlord may grant to Tenant, or if Landlord's
Broker is the procuring cause of any other lease or sale entered into between
Landlord and Tenant covering the Property. Such commission shall be the amount
set forth in Landlord's Broker's commission schedule in effect as of the
execution of this Lease. If a Tenant's Broker is named in Section 1.08 above,
Landlord's Broker shall pay an appropriate portion of its commission Tenant's
Broker if so provided in any agreement between Landlord's Broker and Tenant's
Broker. Nothing contained in this Lease shall impose any obligation on Landlord
to pay a commission or fee to any party other than Landlord's Broker.

         Section 14.02. PROTECTION OF BROKERS. If Landlord sells the Property,
or assigns Landlord's interest in this Lease, the buyer or assignee shall, by
accepting such conveyance of the Property or assignment of the Lease, be
conclusively deemed to have agreed to make all payments to Landlord's Broker
thereafter required of Landlord under this Article Fourteen. Landlord's Broker
shall have the right to bring a legal action to enforce or declare rights under
this provision. The prevailing party in such action shall be entitled to
reasonable attorneys' fees to be paid by the losing party. Such attorneys' fees
shall be fixed by the court in such action. This Paragraph is included in this
Lease for the benefit of Landlord's Broker.

         AGENCY DISCLOSURE; NO OTHER BROKERS. Landlord and Tenant each warrant
that they have dealt with no other real estate broker(s) in connection with this
transaction.

ARTICLE 15 COMPLIANCE

         The parties hereto agree to comply with all applicable federal, state
and local laws, regulations, codes, ordinances and administrative orders having
jurisdiction over the parties, property or the subject matter of this Agreement,
including, but not limited to, the 1964 Civil Rights Act and all amendments
thereto, the Foreign Investment In Real Property Tax Act, the Comprehensive
Environmental Response Compensation and Liability Act, and The Americans With
Disabilities Act.

         ADDITIONAL PROVISIONS MAY BE SET FORTH IN A RIDER OR RIDERS ATTACHED
HERETO OR IN THE BLANK SPACE BELOW. IF NO ADDITIONAL PROVISIONS ARE INSERTED,
PLEASE DRAW A LINE THROUGH THE SPACE BELOW.

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                                                                    CONFIDENTIAL

     Landlord and Tenant have signed this Lease at the place and on the dates
specified adjacent to their signatures below and have Initialed all Riders which
are attached to or incorporated by reference in this Lease.

<Table>
<S>                                                           <C>
                                                                                "LANDLORD"

Signed on   1/10/02                                               Church Ranch Business Center, LLC,
          -------------------------------------------         -----------------------------------------------------
at                                                                a Colorado limited liability company
   --------------------------------------------------         -----------------------------------------------------

                                                              By:      /s/ Gregg A. Bradbury
                                                                 --------------------------------------------------
                                                              Its:     Manager
                                                                  -------------------------------------------------

                                                              By:      /s/ Charles C. McKay  1/10/02
                                                                 --------------------------------------------------
                                                              Its:     Owner / Manager
                                                                  -------------------------------------------------

                                                                   Signed on
                                                                            ---------------------------------------
                                                                   at
                                                                     ----------------------------------------------
                                                                                "TENANT"'

                                                                   Myogen, Inc.,
                                                                   ------------------------------------------------
                                                                   a Colorado corporation
                                                                   ------------------------------------------------

                                                              By:      /s/ J. William Freytag         1-10-02
                                                                 --------------------------------------------------
                                                              Its:
                                                                  -------------------------------------------------

                                                              By:
                                                                 --------------------------------------------------
                                                              Its:
                                                                  -------------------------------------------------
</Table>

         IN ANY REAL ESTATE TRANSACTION, IT IS RECOMMENDED THAT YOU CONSULT WITH
A PROFESSIONAL, SUCH AS A CIVIL ENGINEER, INDUSTRIAL HYGIENIST OR OTHER PERSON
WITH EXPERIENCE IN EVALUATING THE CONDITION OF THE PROPERTY, INCLUDING THE
POSSIBLE PRESENCE OF ASBESTOS, HAZARDOUS MATERIALS AND UNDERGROUND STORAGE
TANKS.

         THIS PRINTED FORM LEASE HAS BEEN DRAFTED BY LEGAL COUNSEL AT THE
DIRECTION OF THE SOUTHERN CALIFORNIA CHAPTER OF THE SOCIETY OF INDUSTRIAL AND
OFFICE REALTORS(R), INC. NO REPRESENTATION OR RECOMMENDATION IS MADE BY THE
SOUTHERN CALIFORNIA CHAPTER OF THE SOCIETY OF INDUSTRIAL AND OFFICE REALTORS(R),
INC., ITS LEGAL COUNSEL, THE REAL ESTATE BROKERS NAMED HEREIN, OR THEIR
EMPLOYEES OR AGENTS, AS TO THE LEGAL SUFFICIENCY, LEGAL EFFECT OR TAX
CONSEQUENCES OF THIS LEASE OR OF THIS TRANSACTION. LANDLORD AND TENANT SHOULD
RETAIN LEGAL COUNSEL TO ADVISE THEM ON SUCH MATTERS AND SHOULD RELY UPON THE
ADVICE OF SUCH LEGAL COUNSEL.

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                                                                   EXHIBIT 10.13

                                                                    CONFIDENTIAL

THIS WARRANT AND THE SHARES ISSUABLE HEREUNDER HAVE BEEN ACQUIRED FOR INVESTMENT
AND HAVE NOT BEEN REGISTERED UNDER THE SECURITIES ACT OF 1933, AS AMENDED, OR
ANY STATE SECURITIES LAWS, AND MAY NOT BE SOLD, PLEDGED, OR OTHERWISE
TRANSFERRED WITHOUT AN EFFECTIVE REGISTRATION THEREOF UNDER SUCH ACT, ANY
APPLICABLE STATE SECURITIES LAWS OR PURSUANT TO RULE 144 OR AN OPINION OF
COUNSEL REASONABLY SATISFACTORY TO THE CORPORATION AND ITS COUNSEL, THAT SUCH
REGISTRATION IS NOT REQUIRED.

                            WARRANT TO PURCHASE STOCK

Corporation: Myogen, Inc.
Number of Shares: 9,091
Class of Stock: Preferred Series C
Initial Exercise Price: $1.375
Issue Date: January 26, 2000
Expiration Date: January 26, 2010

         THIS WARRANT CERTIFIES THAT, for the agreed upon value of $1.00 and for
other good and valuable consideration, SILICON VALLEY BANK ("Holder") is
entitled to purchase the number of fully paid and nonassessable shares of Series
C Preferred Stock (the "Shares") of the corporation (the "Company") at the price
per Share (the "Warrant Price") all as set forth above and as adjusted pursuant
to Article 2 of this Warrant, subject to the provisions and upon the terms and
conditions set forth of this Warrant.

ARTICLE 1.        EXERCISE.

                  1.1      Method of Exercise. Holder may exercise this Warrant
by delivering a duly executed Notice of Exercise in substantially the form
attached as Appendix 1 to the principal office of the Company. Unless Holder is
exercising the conversion right set forth in Section 1.2, Holder shall also
deliver to the Company a check for the aggregate Warrant Price for the Shares
being purchased.

                  1.2      Conversion Right. In lieu of exercising this Warrant
as specified in Section 1.1, Holder may from time to time convert this Warrant,
in whole or in part, into a number of Shares determined by dividing (a) the
aggregate fair market value of the Shares or other securities otherwise issuable
upon exercise of this Warrant minus the aggregate Warrant Price of such Shares
by (b) the fair market value of one Share. The fair market value of the Shares
shall be determined pursuant to Section 1.3.

                  1.3      Fair Market Value. If the Shares are traded in a
public market, the fair market value of the Shares shall be the closing price of
the Shares (or the closing price of the Company's stock into which the Shares
are convertible) reported for the business day immediately before Holder
delivers its Notice of Exercise to the Company. If the Shares are not traded in
a public market, the Board of Directors of the Company shall determine fair
market value in its reasonable good faith judgment. The foregoing
notwithstanding, if Holder advises the Board of Directors in writing that Holder
disagrees with such determination, then the Company and Holder shall promptly
agree upon a reputable investment banking firm to undertake such valuation. If
the valuation of such investment banking firm is greater than that determined by
the Board of Directors, then all fees and expenses of such investment banking
firm shall be paid by the Company. In all other circumstances, such fees and
expenses shall be paid by Holder.

                                        1

<PAGE>

                                                                    CONFIDENTIAL

                  1.4      Delivery of Certificate and New Warrant. Promptly
after Holder exercises or converts this Warrant, the Company shall deliver to
Holder certificates for the Shares acquired and, if this Warrant has not been
fully exercised or converted and has not expired, a new Warrant representing the
Shares not so acquired.

                  1.5      Replacement of Warrants. On receipt of evidence
reasonably satisfactory to the Company of the loss, theft, destruction or
mutilation of this Warrant and, in the case of loss, theft or destruction, on
delivery of an indemnity agreement reasonably satisfactory in form and amount to
the Company or, in the case of mutilation, or surrender and cancellation of this
Warrant, the Company at its expense shall execute and deliver, in lieu of this
Warrant, a new warrant of like tenor.

                  1.6      Sale, Merger, or Consolidation of the Company.

                           1.6.1    "Acquisition". For the purpose of this
Warrant, "Acquisition" means any sale, license, or other disposition of all or
substantially all of the assets of the Company, or any reorganization,
consolidation, or merger of the Company where the holders of the Company's
securities before the transaction beneficially own less than 50% of the
outstanding voting securities of the surviving entity after the transaction.

                           1.6.2    Assumption of Warrant. If upon the closing
of any Acquisition the successor entity assumes the obligations of this Warrant,
then this Warrant shall be exercisable for the same securities, cash, and
property as would be payable for the Shares issuable upon exercise of the
unexercised portion of this Warrant as if such Shares were outstanding on the
record date for the Acquisition and subsequent closing. The Warrant Price shall
be adjusted accordingly. The Company shall use reasonable efforts to cause the
surviving corporation to assume the obligations of this Warrant.

                           1.6.3    Nonassumption. If upon the closing of any
Acquisition the successor entity does not assume the obligations of this Warrant
and Holder has not otherwise exercised this Warrant in full, then the
unexercised portion of this Warrant shall be deemed to have been automatically
converted pursuant to Section 1.2 and thereafter Holder shall participate in the
Acquisition on the same terms as other holders of the same class of securities
of the Company.

ARTICLE 2.        ADJUSTMENTS TO THE SHARES.

                  2.1      Stock Dividends, Splits, Etc. If the Company declares
or pays a dividend on its common stock (or the Shares if the Shares are
securities other than common stock) payable in common stock, or other
securities, subdivides the outstanding common stock into a greater amount of
common stock, or, if the Shares are securities other than common stock,
subdivides the Shares in a transaction that increases the amount of common stock
into which the Shares are convertible, then upon exercise of this Warrant, for
each Share acquired, Holder shall receive, without cost to Holder, the total
number and kind of securities to which Holder would have been entitled had
Holder owned the Shares of record as of the date the dividend or subdivision
occurred.

                  2.2      Reclassification, Exchange or Substitution. Upon any
reclassification, exchange, substitution, or other event that results in a
change of the number and/or class of the securities issuable upon exercise or
conversion of this Warrant, Holder shall be entitled to receive, upon exercise
or conversion of this Warrant, the number and kind of securities and property
that Holder would have received for the Shares if this Warrant had been
exercised immediately before such reclassification, exchange, substitution, or
other event. Such an event shall include any automatic conversion of the
outstanding or issuable securities of the Company of the same class or series as
the Shares to common

                                        2

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                                                                    CONFIDENTIAL

stock pursuant to the terms of the Company's Articles of Incorporation upon the
closing of a registered public offering of the Company's common stock. The
Company or its successor shall promptly issue to Holder a new Warrant for such
new securities or other property. The new Warrant shall provide for adjustments
which shall be as nearly equivalent as may be practicable to the adjustments
provided for in this Article 2 including, without limitation, adjustments to the
Warrant Price and to the number of securities or property issuable upon exercise
of the new Warrant. The provisions of this Section 2.2 shall similarly apply to
successive reclassifications, exchanges, substitutions, or other events.

                  2.3      Adjustments for Combinations, Etc. If the outstanding
Shares are combined or consolidated, by reclassification or otherwise, into a
lesser number of shares, the Warrant Price shall be proportionately increased.

                  2.4      Adjustments for Diluting Issuances. The Warrant Price
and the number of Shares issuable upon exercise of this Warrant or, if the
Shares are Preferred Stock, the number of shares of common stock issuable upon
conversion of the Shares, shall be subject to adjustment, from time to time in
the manner set forth in the Company's Amended and Restated Articles
(Certificate) of Incorporation in effect on the Issue Date.

                  2.5      No Impairment. The Company shall not, by amendment of
its Articles of Incorporation or through a reorganization, transfer of assets,
consolidation, merger, dissolution, issue, or sale of securities or any other
voluntary action, avoid or seek to avoid the observance or performance of any of
the terms to be observed or performed under this Warrant by the Company, but
shall at all times in good faith assist in carrying out of all the provisions of
this Article 2 and in taking all such action as may be necessary or appropriate
to protect Holder's rights under this Article against impairment.

                  2.6      Fractional Shares. No fractional Shares shall be
issuable upon exercise or conversion of the Warrant and the number of Shares to
be issued shall be rounded down to the nearest whole Share. If a fractional
share interest arises upon any exercise or conversion of the Warrant, the
Company shall eliminate such fractional share interest by paying Holder amount
computed by multiplying the fractional interest by the fair market value of a
full Share.

                  2.7      Certificate as to Adjustments. Upon each adjustment
of the Warrant Price, the Company at its expense shall promptly compute such
adjustment, and furnish Holder with a certificate of its Chief Financial Officer
setting forth such adjustment and the facts upon which such adjustment is based.
The Company shall, upon written request, furnish Holder a certificate setting
forth the Warrant Price in effect upon the date thereof and the series of
adjustments leading to such Warrant Price.

ARTICLE 3.        REPRESENTATIONS AND COVENANTS OF THE COMPANY.

                  3.1      Representations and Warranties. The Company hereby
represents and warrants to the Holder as follows:

                           (a)      The initial Warrant Price referenced on the
first page of this Warrant is not greater than the price per share at which the
Shares were last issued in an arms-length transaction in which at least $500,000
of the Shares were sold.

                           (b)      All Shares which may be issued upon the
exercise of the purchase right represented by this Warrant, and all securities,
if any, issuable upon conversion of the Shares, shall, upon issuance, be duly
authorized, validly issued, fully paid and nonassessable, and free of any liens
and

                                        3

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                                                                    CONFIDENTIAL

encumbrances except for restrictions on transfer provided for herein or under
applicable federal and state securities laws.

                  3.2      Notice of Certain Events. If the Company proposes at
any time (a) to declare any dividend or distribution upon its common stock,
whether in cash, property, stock, or other securities and whether or not a
regular cash dividend; (b) to offer for subscription pro rata to the holders of
any class or series of its stock any additional shares of stock of any class or
series or other rights; (c) to effect any reclassification or recapitalization
of common stock; (d) to merge or consolidate with or into any other corporation,
or sell, lease, license, or convey all or substantially all of its assets, or to
liquidate, dissolve or wind up; or (e) offer holders of registration rights the
opportunity to participate in an underwritten public offering of the company's
securities for cash, then, in connection with each such event, the Company shall
give Holder (1) at least 20 days prior written notice of the date on which a
record will be taken for such dividend, distribution, or subscription rights
(and specifying the date on which the holders of common stock will be entitled
thereto) or for determining rights to vote, if any, in respect of the matters
referred to in (c) and (d) above; (2) in the case of the matters referred to in
(c) and (d) above at least 20 days prior written notice of the date when the
same will take place (and specifying the date on which the holders of common
stock will be entitled to exchange their common stock for securities or other
property deliverable upon the occurrence of such event); and (3) in the case of
the matter referred to in (e) above, the same notice as is given to the holders
of such registration rights.

                  3.3      Information Rights. So long as the Holder holds this
Warrant and/or any of the Shares, the Company shall deliver to the Holder (a)
promptly after mailing, copies of all notices or other written communications to
the shareholders of the Company, (b) within ninety (90) days after the end of
each fiscal year of the Company, the annual audited financial statements of the
Company certified by independent public accountants of recognized standing and
(c) within forty-five (45) days after the end of each of the first three
quarters of each fiscal year, the Company's quarterly, unaudited financial
statements.

                  3.4      Registration Under Securities Act of 1933, as
amended. The Company agrees that the Shares or, if the Shares are convertible
into common stock of the Company, such common stock, shall be subject to the
registration rights set forth on Exhibit A.

ARTICLE 4.        MISCELLANEOUS.

                  4.1      Term; Notice of Expiration. This Warrant is
exercisable, in whole or in part, at any time and from time to time on or before
the Expiration Date set forth above.

                  4.2      Legends. This Warrant and the Shares (and the
securities issuable, directly or indirectly, upon conversion of the Shares, if
any) shall be imprinted with a legend in substantially the following form in
addition to any legends required pursuant to the Second Amended and Restated
Investors' Rights Agreement dated as of November ___, 1999, by and between
Company and the investors named therein.

         THIS SECURITY HAS NOT BEEN REGISTERED UNDER THE SECURITIES ACT OF 1933,
         AS AMENDED, AND MAY NOT BE SOLD, PLEDGED OR OTHERWISE TRANSFERRED
         WITHOUT AN EFFECTIVE REGISTRATION THEREOF UNDER SUCH ACT OR PURSUANT TO
         RULE 144 OR AN OPINION OF COUNSEL REASONABLY SATISFACTORY TO THE
         CORPORATION AND ITS COUNSEL THAT SUCH REGISTRATION IS NOT REQUIRED.

                                        4

<PAGE>

                                                                    CONFIDENTIAL

                  4.3      Compliance with Securities Laws on Transfer. This
Warrant and the Shares issuable upon exercise this Warrant (and the securities
issuable, directly or indirectly, upon conversion of the Shares, if any) may not
be transferred or assigned in whole or in part without compliance with
applicable federal and state securities laws by the transferor and the
transferee (including, without limitation, the delivery of investment
representation letters and legal opinions reasonably satisfactory to the
Company, as reasonably requested by the Company). The Company shall not require
Holder to provide an opinion of counsel if the transfer is to an affiliate of
Holder or if there is no material question as to the availability of current
information as referenced in Rule 144(c), Holder represents that it has complied
with Rule 144(d) and (e) in reasonable detail, the selling broker represents
that it has complied with Rule 144(f), and the Company is provided with a copy
of Holder s notice of proposed sale.

                  4.4      Transfer Procedure. Subject to the provisions of
Section 4.3 Holder may transfer all or part of this Warrant or the Shares
issuable upon exercise of this Warrant (or the securities issuable, directly or
indirectly, upon conversion of the Shares, if any) at any time to Silicon Valley
Bancshares or The Silicon Valley Bank Foundation by giving the Company notice of
the portion of the Warrant being transferred setting forth the name, address and
taxpayer identification number of the transferee and surrendering this Warrant
to the Company for reissuance to the transferee(s) (and Holder if applicable).
Unless the Company is filing financial information with the SEC pursuant to the
Securities Exchange Act of 1934, the Company shall have the right to refuse to
transfer any portion of this Warrant to any person who directly competes with
the Company.

                  4.5      Notices. All notices and other communications from
the Company to the Holder, or vice versa, shall be deemed delivered and
effective when given personally or mailed by first-class registered or certified
mail, postage prepaid, at such address as may have been furnished to the Company
or the Holder, as the case may be, in writing by the Company or such holder from
time to time.

                  4.6      Waiver. This Warrant and any term hereof may be
changed, waived, discharged or terminated only by an instrument in writing
signed by the party against which enforcement of such change, waiver, discharge
or termination is sought.

                  4.7      Attorneys Fees. In the event of any dispute between
the parties concerning the terms and provisions of this Warrant, the party
prevailing in such dispute shall be entitled to collect from the other party all
costs incurred in such dispute, including reasonable attorneys' fees.

                  4.8      Governing Law. This Warrant shall be governed by and
construed in accordance with the laws of the State of California, without giving
effect to its principles regarding conflicts of law.

                                           MYOGEN, INC.

                                           By: /s/ J. William Freytag
                                               ---------------------------------
                                           Title: President & CEO
                                                  ------------------------------
                                                   (Print)

                                        5

<PAGE>

                                                                    CONFIDENTIAL

                                   APPENDIX 1

                               NOTICE OF EXERCISE

1.       The undersigned hereby elects to purchase ________ shares of the
Common/Series ___ Preferred [strike one] Stock of ____________________ pursuant
to the terms of the attached Warrant, and tenders herewith payment of the
purchase price of such shares in full.

1.       The undersigned hereby elects to convert the attached Warrant into
Shares/cash [strike one] in the manner specified in the Warrant. This conversion
is exercised with respect to ____________________ of the Shares covered by the
Warrant.

         [Strike paragraph that does not apply.]

2.       Please issue a certificate or certificates representing said shares in
the name of the undersigned or in such other name as is specified below:

                                     (Name)

                                    (Address)

3.       The undersigned represents it is acquiring the shares solely for its
own account and not as a nominee for any other party and not with a view toward
the resale or distribution thereof except in compliance with applicable
securities laws.

                                   (Signature)

__________________
(Date)

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<PAGE>

                                                                    CONFIDENTIAL

                                    EXHIBIT A

                               Registration Rights

         The Shares or the common stock issuable upon conversion of the Shares,
shall be deemed to be Registrable Securities (as defined in the Second Amended
and Restated Investor Rights Agreement by and among the Company and certain
Investors, dated as of November __, 1999, the "Rights Agreement") for purposes
of Sections 2.1, 2.3, 2.4, 2.5, 2.6, 2.7, 2.8, 2.9, 2.10, 2.12 and 2.13 of the
Rights Agreement, otherwise entitled "piggy back" registration rights.

         The Company and Holder agree that no amendments will be made to the
Rights Agreement which adversely affects the rights granted to Holder hereunder
unless such amendment(s) adversely affect all Series C Preferred Holders.

                                        7

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