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                                                                    EXHIBIT 10.1

                            SECOND AMENDMENT TO LEASE


         THIS SECOND AMENDMENT TO LEASE (this "Second Amendment") is effective
as of April 1, 2001 (the "Effective Date") by and between AMGEN INC., a Delaware
corporation ("Sublandlord"), and ARRAY BIOPHARMA INC., a Delaware corporation
("Subtenant").

                                    RECITALS

         A. Sublandlord and Subtenant are parties to that certain Lease dated
July 7, 1998, as amended by First Amendment to Lease dated April 1, 1999 (the
"Lease"), pursuant to which Subtenant leases a portion of the premises commonly
known as Amgen Buildings AC 1-4 of the "Amgen Complex" located at 3200 Walnut
Street, Boulder, Colorado, as more particularly set forth in the Lease.

         B. On May 13, 1999, Sublandlord and Boulder Headquarters LLC ("Master
Lease Landlord") entered into a transaction in which (i) Sublandlord conveyed
the Amgen Complex to Master Lease Landlord, and (ii) Sublandlord leased the
Amgen Complex from Master Lease Landlord pursuant to that certain Lease dated
May 13, 1999 (the "Master Lease").

         C. In connection with such transaction, Subtenant executed and
delivered to Sublandlord and Master Lease Landlord a Subordination,
Nondisturbance and Attornment Agreement dated May 13, 1999 (the "SNDA"), which
provides for, among other matters, the subordination of the Lease to the Master
Lease and the parties' acknowledgment that the Lease became a sublease of the
Master Lease. Therefore, the Lease shall be hereinafter referred to as the
"Sublease."

         D. Concurrently herewith, Sublandlord and Master Lease Landlord have
entered into that certain First Amendment to Lease amending the Master Lease
(the "First Amendment"), a copy of which is attached hereto as Exhibit A. As
hereinafter used, the term "Master Lease" includes the First Amendment.

         E. Sublandlord and Subtenant desire to amend the Sublease to (i)
confirm the parties' understanding that the Sublease is a sublease of the Master
Lease, (ii) extend the Term, and (iii) modify the Sublease in certain other
respects as provided herein.

         F. Initially capitalized terms used and not defined herein have the
meanings given to such terms in the Sublease.



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                                    AGREEMENT

         NOW THEREFORE, for other good and valuable consideration, the receipt
and sufficiency of which are hereby acknowledged, Sublandlord and Subtenant
hereby agree as follows:

         1. Basic Provisions. The Basic Provisions are hereby amended as
follows:

                  i. Delete the words "Three years" under the heading "Initial
         Term" and reference Section 5.a in their place.

                  ii. Add the following as paragraphs l, m and n, respectively:

                          "l.       Master Lease: Lease between Boulder
                                    Headquarters LLC and Amgen Inc. dated May
                                    13, 1999

                           m.       Master Lease Landlord: Boulder Headquarters
                                    LLC

                           n.       Second Amendment: That certain Second
                                    Amendment to Lease between Landlord and
                                    Tenant dated as of the Effective Date (as
                                    defined below)"

         2. Term.

                  i. Section 5.a of the Sublease is hereby amended to delete
         such section in its entirety and to replace it with the following: "The
         term of this Lease (the "Term") shall commence on the Commencement Date
         and terminate at midnight on the day immediately preceding the seventh
         anniversary of April 1, 2001 (the "Effective Date"), unless sooner
         terminated in accordance with the terms of this Lease."

                  ii. Section 5.b of the Sublease is hereby amended to delete
         such section in its entirety.

         3. Monthly Rent.

                  i. The Basic Provisions are hereby amended to add the
         following under the heading "Rent:" "Commencing on the Effective Date,
         the Rent shall be $25.00 per square foot of the Premises per annum,
         subject to annual adjustment in accordance with Exhibit B."

                  ii. Exhibit B to the Sublease is hereby amended to delete the
         dates under the heading "Period" in Paragraph A to replace them with
         "7/15/98 - The day immediately preceding the Effective Date."


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                  iii. The text of Paragraph B of Exhibit B to the Sublease is
         hereby deleted in its entirety and replaced with the following:

                           The Rent shall be increased on each anniversary of
                           the Effective Date (and shall be effective for each
                           successive Lease year) by taking the monthly base
                           rent payable at the end of the immediately preceding
                           Lease year and adding to that number the amount
                           determined by multiplying the monthly base rent by
                           three percent (3%).

         4. Additional Rent. Section 8.b of the Sublease is hereby amended to
delete the first three sentences of such section and to replace them with the
following:

                  Any costs that Tenant is required to pay under this Lease
                  shall become "Additional Rent" due under this Lease.
                  Additional Rent shall be due to Landlord with the next
                  installment of Rent due, or if no installment of Rent is due,
                  within 15 days following receipt by Tenant of a written
                  invoice of such costs. Additional Rent may include, but is not
                  limited to, Tenant's pro rata share of (i) all Additional Rent
                  due under the Master Lease, and (ii) all amounts incurred by
                  Landlord in connection with the Premises (exclusive of costs
                  attributable solely to any portion of any building reserved
                  for the exclusive use of Landlord), including, without
                  limitation, all costs to maintain, repair and replace the
                  mechanical, electrical, elevator, HVAC, fire monitoring,
                  sprinkler and building management systems; modifications
                  requested by Tenant to any system used in the Amgen Complex
                  that affects the Premises; (iii) costs of capital
                  improvements, major structural repairs, boiler replacement and
                  other capital replacements, and major roof repairs, provided,
                  however, that Additional Rent for any such item shall be
                  amortized over such item's projected useful life only if and
                  to the extent the Additional Rent for any such item is
                  likewise amortized under the Master Lease, and not otherwise;
                  and (iv) insurance and real property taxes and assessments for
                  the Premises; parking lot maintenance (including, without
                  limitation, snowplowing and sweeping); and landscaping care
                  and irrigation.

         5. Maintenance. Section 9 of the Sublease is hereby amended to add the
following as Section 9.e:

                  e. Tenant's Assumption of Maintenance Obligations.
         Notwithstanding anything in this Lease to the contrary, Tenant shall
         assume and perform, at its sole cost and expense, all obligations of
         "Tenant" (as defined in the Master Lease) under Section 7 and Section
         11.1 of the Master Lease and of Landlord under Section 9 of this Lease,
         except those obligations for parking lot maintenance, sprinkler system
         maintenance and landscaping (collectively, the



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         "Obligations"), according to the following schedule: (i) as of the
         Effective Date, Tenant shall assume and perform the Obligations for
         Buildings AC-1 and AC-4, and (ii) as of the date on which Tenant
         possesses the majority of the square footage contained within either
         Building AC-2, Building AC-3 or the area known as the "Bridge," Tenant
         shall assume and perform the Obligations for such buildings and/or
         Bridge, as applicable. In the event that Landlord possesses any portion
         of any building or Bridge during the period in which Tenant is required
         to perform the Obligations, Landlord shall reimburse Tenant, on an
         annual basis, Landlord's pro rata share of the costs incurred by Tenant
         to perform the Obligations (exclusive of costs attributable solely to
         any portion of any building reserved for the exclusive use of Tenant).
         Such reimbursement shall be (y) made in accordance with the provisions
         of Section 8.b (excluding any provision related to the timing of
         payment) and (z) subject to Landlord's receipt and approval of a
         statement summarizing such costs, together with supporting invoices.
         Tenant shall promptly and diligently perform the Obligations and all
         other maintenance, repair and replacement work for which it is
         responsible.

                  Pursuant to the report entitled "Physical Condition Review --
         Amgen Buildings 1-4, 3200 Walnut Street, Boulder, Colorado" prepared by
         Reidenbaugh Associates, LLC dated February 12, 2001 (the "Report"), the
         roof for Building AC-3 has an approximate remaining useful life of two
         to four years from the Effective Date. Within ten (10) business days
         following the Effective Date, Landlord shall establish an escrow
         account containing funds to replace the roof (the "Funds"). If the roof
         has not been replaced prior to the date on which Tenant takes
         possession of Building AC-3, the Funds shall be made available to
         Tenant pursuant to an assignment of the escrow agreement between
         Landlord and Tenant, and Tenant covenants to replace the roof in
         accordance with the terms of the Master Lease prior to the expiration
         of the Term of this Lease.

                  Notwithstanding the foregoing or anything in this Lease to the
         contrary, effective on the date that Tenant takes possession of the
         entire Amgen Complex in accordance with the Expansion Schedule set
         forth in Exhibit B to the Second Amendment or pursuant to Section 9 of
         the Second Amendment, Tenant shall assume and thereafter perform, at
         its sole cost and expense (except as otherwise provided in the
         immediately preceding paragraph), all obligations of "Tenant" (as
         defined in the Master Lease) under Section 7 and Section 11.1 of the
         Master Lease and of Landlord under Section 9 of this Lease, and in such
         event, the costs and expenses incurred by Tenant to perform such
         obligations shall not be charged to Tenant as Additional Rent.

         6. Expansion of Premises. Section 6 of the Sublease is hereby amended
to delete such section in its entirety and to replace it with the following:

                  a. Expansion. As of March 1, 2001, the Premises shall be
         expanded to include the space cross-hatched in Exhibit C attached to
         the Second Amendment located in Building AC-4 and consisting of
         approximately 4,000 square feet.



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                  In accordance with the Expansion Schedule set forth in Exhibit
         B attached to the Second Amendment, the Premises shall be expanded
         during the Term to include 143,900 square feet of rentable space in
         Buildings AC-1, the Bridge, AC-2, AC-3 and AC-4, together with the
         parking areas, associated driveways and landscaping comprising the
         Amgen Complex, all of which includes the entire Premises demised under
         the Master Lease. If Tenant desires to take possession of Expansion
         Spaces "B," "C," "D," and/or "E" prior to the Expansion Dates for such
         spaces set forth in the left-hand column of the Expansion Schedule
         (individually, an "Expansion Date," and collectively, the "Expansion
         Dates"), in accordance with the early election periods noted on the
         Expansion Schedule, Tenant shall provide Landlord with six months'
         prior written notice. In the event of any such early possession, the
         date on which Tenant is to take possession shall be deemed to be the
         Expansion Date for such Expansion Space.

                  With respect to Expansion Space "C" and Expansion Space "E,"
         Tenant may elect to take possession of such spaces as early as May 1,
         2003, on the condition that Tenant first obtains Landlord's prior
         written consent. If Landlord does not consent to the May 1 date, then
         Tenant may not take possession of such spaces until, at the earliest,
         July 1, 2003.

                  Landlord shall use reasonable efforts to allow Tenant access
         to the applicable Expansion Space 30 days prior to any applicable
         Expansion Date to permit Tenant to commence construction of any tenant
         improvements to the Expansion Space, as approved by Landlord in
         accordance with the terms of this Lease and Master Lease Landlord in
         accordance with the terms of the Master Lease. During such 30-day
         period, Tenant's use and possession of the Expansion Space shall be
         subject to all of the terms and conditions of this Sublease, except for
         the payment of Rent.

                  On March 1, 2001, with respect to the space cross-hatched in
         Exhibit C attached to the Second Amendment and on the applicable
         Expansion Date with respect to any Expansion Space (provided that
         Landlord has delivered the Expansion Space to Tenant), all references
         in this Lease to the term "Premises" shall be deemed to include such
         space for all purposes for the balance of the Term, upon and subject to
         all of the terms, covenants and conditions of this Lease without the
         need for further action by Landlord or Tenant.

                  b. Delivery of Expansion Space. Landlord will deliver the
         Expansion Space to Tenant on the applicable Expansion Date. If the
         Expansion Space is not delivered to Tenant within 30 days following the
         applicable Expansion Date (including any early possession date, if
         applicable), Tenant shall be entitled to receive from Landlord
         liquidated damages in an amount equal to three (3) times Tenant's daily
         Rent (excluding Additional Rent) with respect to the Expansion



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         Space for each day in excess of 30 days that Landlord delays in
         delivering the Expansion Space to Tenant. Landlord and Tenant
         acknowledge that the damages incurred by Tenant due to any delay in
         delivery of the Expansion Space will be difficult to calculate and the
         parties agree that the foregoing liquidated damages are a reasonable
         estimate of such damages. Landlord shall pay any amount due hereunder
         monthly, in arrears. If the Expansion Space is not delivered to Tenant
         within 90 days following the applicable Expansion Date (including any
         early possession date, if applicable), Tenant shall be entitled to
         terminate the parties' rights and obligations under this Lease with
         respect to the Expansion Space for which delivery is delayed by giving
         written notice to Landlord within 10 days following the expiration of
         such 90-day period, and in such event, Tenant shall have no further
         rights or interest in such space and Landlord shall be free to lease
         such space to another tenant. The foregoing remedies shall be Tenant's
         sole and exclusive remedies for a delay in the delivery of the
         Expansion Space, and Landlord shall not be deemed to be in default
         under this Lease, and shall not be liable for any other claims, damages
         or liabilities, due to such failure to deliver any Expansion Space.

                  Subject to Tenant's termination rights set forth in the
         immediately preceding paragraph, this Lease (as amended by the Second
         Amendment) shall remain in full force and effect despite any failure of
         Landlord to deliver the Expansion Space. If Landlord is unable to
         deliver the Expansion Space to Tenant on or before the applicable
         Expansion Date due to Tenant's acts or omissions, Tenant shall not be
         entitled to receive liquidated damages from Landlord. If Tenant is
         unable or unprepared to occupy any Expansion Space on the applicable
         Expansion Date, Rent for such Expansion Space shall commence on the
         earlier of Tenant's occupancy of such space or the date that is 30 days
         following the Expansion Date; provided, however, that under no
         circumstances shall Tenant be obligated to pay Rent for any Expansion
         Space until Landlord tenders possession of such Expansion Space to
         Tenant.

                  c. Rent - Expansion Space. Subject to the terms of Section 6.b
         above, commencing on the applicable Expansion Date, Tenant shall pay
         Rent for the Expansion Space in accordance with Section 3 of the Second
         Amendment and the terms of this Lease.

                  d. Office Furniture. If Tenant desires to lease any of
         Landlord's office furniture located in any Expansion Space, the parties
         shall negotiate the terms of such rental prior to Tenant's acceptance
         of such Expansion Space (with neither party being obligated to agree to
         such rental), and the Rent shall be increased accordingly, but in no
         event more than $.50 per square foot per annum for the Expansion Space
         containing such furniture.

                  e. Parking. Upon delivery of an Expansion Space to Tenant,
         Tenant's parking space allocation shall be proportionately increased
         with each such expansion based on the square footage of such Expansion
         Space, with any


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         remainder being rounded down. Landlord and Tenant acknowledge that
         there are no assigned or exclusive parking areas or spaces.

         7. Security Deposit. Section 7 of the Sublease is hereby amended to add
the following as Section 7.c:

                  c. Additional Security Deposits. On or before April 5, 2001
         with respect to the space cross-hatched in Exhibit C attached to the
         Second Amendment and at least 30 days prior to each Expansion Date,
         Tenant shall deliver to Landlord an additional security deposit in the
         form of a clean, unconditional, irrevocable letter of credit or
         certificate of deposit for the benefit of Landlord in the amount of six
         times the Monthly Base Rent applicable to such Expansion Space. Such
         additional security deposit shall (i) meet all requirements of this
         Section 7, and (ii) secure Tenant's faithful performance of its
         obligations under this Lease. Within five (5) business days following
         the date of the assignment of the Master Lease to Tenant pursuant to
         Section 9 of this Lease, Landlord shall inspect the Premises and shall
         notify Tenant if any portion of the Security Deposit will be retained
         by Landlord in accordance with the terms of Section 7.b of this Lease.
         Upon the condition that Landlord shall have received the release
         referenced in Section 9.b of the Second Amendment (if applicable) and
         to the extent such security deposit has not been used by Landlord in
         accordance with the terms of Section 7.b of this Lease, within five (5)
         business days following Landlord's notice to Tenant, such security
         deposit shall, at Tenant's option, either be delivered to Tenant or
         assigned to Master Lease Landlord to secure Tenant's obligations as
         tenant under the Master Lease in accordance with the terms of Section 9
         of the Second Amendment or to secure Tenant's obligations under the new
         lease to be entered into between Master Lease Landlord and Tenant upon
         the expiration of the Master Lease, as applicable.

         8. Alterations/Modifications.

                  i. Section 10.c of the Sublease is hereby amended to add the
         following at the end of such section:

                  Notwithstanding anything in this Lease to the contrary, Tenant
                  shall have the right to remove trade fixtures, including,
                  without limitation, hoods, casework, laboratory and supporting
                  equipment, from the Premises without the consent of Landlord,
                  subject to the conditions that (a) such trade fixtures are
                  listed on the bill of sale executed by Landlord and Master
                  Lease Landlord of even date herewith (the "Bill of Sale") or
                  were installed by Landlord or Tenant after the date of the
                  Master Lease, and (b) such removal will not reduce the overall
                  value of the improvements to the Premises from that existing
                  on the date of the Master Lease, less the value of the
                  equipment and fixtures



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                  described in such Bill of Sale. If Tenant elects to remove any
                  of the foregoing items, Tenant shall be required to repair any
                  incidental damage caused by such removal.

                  Landlord acknowledges that Tenant intends to convert portions
                  of the Premises into chemistry laboratories and that such
                  laboratories are included as a permitted use of the Premises.
                  Landlord agrees to reasonably cooperate with such conversion
                  and to use reasonable efforts to obtain consent from Master
                  Lease Landlord with respect to such conversion, subject in all
                  respects to the terms of this Lease and the Master Lease
                  regarding alterations and modifications to the Premises.

         9. Sublease/Assignment.

                  Section 17 of the Sublease is hereby amended to add the
         following at the end of such section:

                  If at any time following the fifth anniversary of the
         Effective Date Landlord desires to be released from its obligations as
         tenant under the Master Lease arising on or after the date of
         assignment, Tenant or its successors or permitted assigns ("Assignee")
         shall assume all of Landlord's rights and obligations under the Master
         Lease, subject to the satisfaction of each of the following conditions:

                           a. Assignee and Landlord shall execute and deliver an
                  assignment and assumption of the Master Lease in form and
                  substance reasonably acceptable to the parties and Master
                  Lease Landlord;

                           b. Master Lease Landlord shall execute and deliver to
                  Tenant a full and unconditional release releasing Landlord
                  from all obligations as tenant under the Master Lease arising
                  on or after the date of assignment in form and substance
                  reasonably acceptable to Landlord and Master Lease Landlord;

                           c. Assignee shall have a tangible net worth (i.e.
                  total stockholders' equity shown on the most recent balance
                  sheet) of not less than $400 million;

                           d. Assignee shall have reported profitability for the
                  two prior years of not less than $25 million annually;

                           e. Concurrently with the assignment of the Master
                  Lease, Assignee shall post a security deposit (in the form of
                  an irrevocable letter of credit or cash) in an amount equal to
                  six months' Rent under the Master Lease. Within ten business
                  days following the date of such assignment,



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                  Assignee shall increase the security deposit by an additional
                  six months' rent under the Master Lease, so that the total
                  security deposit held by Landlord to secure Assignee's
                  obligations under the Master Lease equals twelve months' rent
                  under the Master Lease; and

                           f. As of the date of the assignment, Landlord shall
                  not be in default under the Master Lease nor shall Assignee be
                  in default under this Lease beyond any applicable notice and
                  cure period.

         10. Default. Section 21.b of the Sublease is hereby amended to add the
following at the end of such section:

                  iii. If Tenant fails to perform, within 15 days following
         notice from Landlord, any obligation required to be performed by Tenant
         under this Lease other than the payment of Rent, including, without
         limitation, any obligation to maintain, repair or replace any portion
         of the Premises, then Landlord shall have the right (but shall not be
         obligated), either by itself or through a third party, to perform such
         obligation, and in such event, Tenant shall pay to Landlord, on demand,
         the cost thereby incurred by Landlord plus 10% for administrative
         costs.

         11. Condition of Premises. Sublandlord shall not be responsible for
performing any renovations or tenant improvements to the Premises in connection
with this Second Amendment. Subtenant agrees to accept the Premises, as the same
may be constituted from time to time in accordance with the addition of the
Expansion Spaces, in their "AS-IS" condition with all faults, subject to
Sublandlord's obligations set forth in Section 5 of this Second Amendment and
Sections 8.1, 10 and Exhibit C of the Master Lease that pertain solely to
vacation of the Premises. Notwithstanding the foregoing, Landlord and Tenant
acknowledge that the Report states that the Fulton Boiler is currently out of
service and that the cooling tower located in Building AC-2 (the "Cooling
Tower") has a maximum estimated life of 2 to 3 years. The provisions of Section
8.1 of the Master Lease shall not be construed to create any obligation on the
part of Landlord to repair or to replace the Fulton Boiler or the Cooling Tower
upon its vacation of the Premises.

         12. Insurance.

                  i. Section 13 of the Sublease is hereby amended to delete the
         text of such section in its entirety and to replace it with the
         following:

                  Tenant shall, at Tenant's expense, maintain during the Term of
                  this Lease the following insurance:

                           a. Commercial general liability, bodily injury and
                  property damage comprehensive coverage insuring against
                  injury, death or property damage, with a combined single limit
                  coverage of not less than $2,000,000 per occurrence with a
                  $3,000,000 general aggregate on an annual basis,



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                  and with a maximum deductible of not more than $10,000, which
                  shall include a provision for contractual liability coverage
                  insuring Tenant for the performance of its indemnity
                  obligations set forth in this Lease and excess liability
                  coverage of not less than $10,000,000 on an annual basis.

                           b. All risk personal property insurance for the full
                  replacement value of all fixtures, equipment, furniture and
                  inventory on the Premises.

                           c. All risk property insurance covering Building AC-1
                  for the full replacement of Building AC-1 and all fixtures
                  attached thereto.

                           d. Workers' compensation insurance to the statutory
                  limit and employer's liability insurance to the limit of
                  $1,000,000 per occurrence; and

                           e. Automobile liability coverage, including coverage
                  for hired and non-owned automobiles, with a combined single
                  limit coverage of not less than $1,000,000 per occurrence on
                  an annual basis, and with a maximum deductible of not more
                  than $10,000.

                  Insurance required hereunder shall be provided by companies
         with a Best's Insurance Guide Rating of "A" or better. Tenant shall
         deliver to landlord copies of insurance policies required herein or
         certificates evidencing the existence and amounts of such insurance
         with loss payable clauses satisfactory to Landlord within ten (10)
         business days prior to occupancy of the Premises (including any
         Expansion Space), and shall provide to Landlord copies of all renewals
         thereof. No policy shall be cancelable or subject to material change or
         reduction of coverage without 60 days' prior written notice to
         Landlord, and the certificate shall so state. All such policies shall
         be written as primary policies not contributing with and not in excess
         of coverage which Landlord may carry. Landlord shall be named as an
         additional insured on all policies required herein. In addition to
         Landlord being named as an additional insured on all policies required
         herein (excluding policies for workers' compensation coverage), such
         policies shall also name Landlord's directors, officers, employees,
         agents, subsidiaries and management companies as additional insureds.
         Landlord shall not be responsible for, and Tenant releases and
         discharges Landlord from, and Tenant further waives any right of
         recovery from Landlord for, any loss from business interruption or loss
         of use of the Premises suffered by Tenant in connection with Tenant's
         use or occupancy of the Premises, even if such loss is caused solely or
         in part by the negligence of Landlord.

                  ii. With respect to any increases in the foregoing coverages
         in connection with this Second Amendment, Tenant shall deliver copies
         of such policies or certificates to Landlord within ten (10) business
         days following the Effective Date.



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         13. Master Lease. This Sublease is and shall at all times continue to
be subject and subordinate to the Master Lease. All of the terms, provisions,
covenants and conditions of the Master Lease are incorporated herein by
reference and are hereby made a part of the Sublease, except to the extent that
they are inconsistent with a term or provision of the Sublease and except that
Subtenant shall be obligated to pay only the monthly Rent and Additional Rent
provided for in the Sublease. Subtenant acknowledges that it has received a copy
of the Master Lease and that it is familiar with the contents thereof. Subtenant
covenants and agrees that it will not do anything that, following any applicable
notice and cure period, would constitute a default under the Master Lease or
omit to do anything that it is obligated to do under the terms of the Sublease
and that, following any applicable notice and cure period, would constitute a
default under the Master Lease.

         14. Termination of Master Lease. In the event of a termination of the
Master Lease or Sublandlord's right to possession of the Premises, this Sublease
shall terminate coincidentally therewith and Sublandlord and Subtenant shall be
relieved of all obligations under this Sublease arising subsequent to the date
of such termination. Any rights of Subtenant with respect to the Premises
following such termination shall exist only under or by virtue of the terms of
the SNDA and/or any separate agreement between Subtenant and Master Lease
Landlord. Sublandlord covenants that it shall not voluntarily terminate the
Master Lease or enter into an agreement with Master Lease Landlord to terminate
the Master Lease prior to the expiration of the Sublease.

         15. Signage. Subject to the terms and conditions of the Sublease and
the Master Lease, Tenant, at its expense, shall be entitled to change all
signage facing Walnut Street to reflect Tenant's occupancy of the Premises.
Tenant shall be solely responsible for obtaining all City approvals and permits
in connection with any changes to the signage. Notwithstanding the foregoing,
Landlord, at its expense, shall be entitled to place signage on Building AC-4,
as necessary in the parties' reasonable determination, to direct visitors to
Landlord's space.

         16. Binding Effect. All of the terms and provisions of the Sublease, as
herein amended and supplemented, are hereby ratified and confirmed, and shall
remain in full force and effect and shall be binding upon the parties hereto,
their successors and assigns. Except as contemplated by this Second Amendment,
all of the terms and provisions of the SNDA are hereby ratified and confirmed
and shall remain in full force and effect and shall be binding upon the parties
hereto, their successors and assigns. This Second Amendment shall become
effective only after the full execution and delivery hereof by Sublandlord and
Subtenant.

         17. Conflict. In the event of any conflict between the provisions of
this Second Amendment and the provisions of the other portions of the Sublease,
the



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provisions of this Second Amendment shall control. All references herein to the
Sublease shall be as amended by this Second Amendment.

         18. No Brokers. Sublandlord and Subtenant each represent and warrant to
the other that they have not engaged or dealt with any broker in connection with
this Second Amendment. Sublandlord and Subtenant each agree to indemnify and
hold the other harmless from and against any cost (including reasonable
attorneys' fees and court costs), expenses, claims, commissions and actions
arising from the falsity or alleged falsity of the foregoing representation.

         19. Miscellaneous. Time is of the essence with respect to this Second
Amendment. This Second Amendment represents the final expression of the
agreement between the parties relating to the subject matter hereof and
supersedes all prior agreements, understandings, discussions and negotiations,
oral or written, regarding the subject matter hereof. A condition precedent to
the effectiveness of this Second Amendment shall be the execution by all parties
and delivery of: (i) the First Amendment to Loan Agreement and Loan Documents,
between Master Lease Landlord and Sublandlord, (ii) the Bill of Sale, from
Master Lease Landlord, (iii) the First Amendment to Lease, between Master Lease
Landlord and Sublandlord, and (iv) the Escrow Agreement between Subtenant and
Sublandlord. No provision hereof can be modified or waived except in a writing
signed by the parties. The successful party in any action brought under this
Second Amendment shall be entitled to an award of reasonable attorneys' fees,
costs and other expenses incurred in such action. This Second Amendment may be
executed in two or more counterparts, each of which shall be deemed an original,
and all of which together shall constitute one and the same instrument.

                         [SIGNATURES ON FOLLOWING PAGE]









                                       12
<PAGE>   13



         Sublandlord and Subtenant have executed this Second Amendment to be
effective as of the date set forth above.

                                  "LANDLORD" AND "SUBLANDLORD":

                                  AMGEN INC., a Delaware corporation


                                  By: /s/ Sarah M. Jensen
                                      ------------------------------------------

                                  Name: Sarah M. Jensen
                                        ----------------------------------------

                                  Title: VP-EOS
                                         ---------------------------------------


                                  "TENANT" AND "SUBTENANT":

                                  ARRAY BIOPHARMA INC., a Delaware
                                  corporation


                                  By: /s/ Michael Carruthers
                                      ------------------------------------------

                                  Name: Michael Carruthers
                                        ----------------------------------------

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






                                       13
<PAGE>   14


                                    EXHIBIT A
               (Executed Copy of First Amendment to Master Lease)


                            FIRST AMENDMENT TO LEASE

         THIS FIRST AMENDMENT TO LEASE (this "First Amendment") is entered into
as of the 1st day of April, 1999, by and between AMGEN INC., a Delaware
corporation ( "Landlord") and ARRAY BIOPHARMA INC., a Delaware corporation
("Tenant").

                                    RECITALS:

         A. On or about July 7, 1998, Landlord and Tenant entered into that
certain Lease (the "Lease"), covering certain space commonly known as Amgen
Building AC-1 of the Amgen Complex and located at 1885 33rd Street, Boulder,
Colorado (the "Premises").

         B. Tenant has requested: (i) to enlarge the Premises by leasing an
additional 3,931 rentable square feet located on the bridge of the Amgen
Complex, as shown on Exhibit A attached hereto (the "Expansion Space"); and (ii)
to further amend and modify the Lease in certain respects as provided herein,
and Landlord has agreed to such modifications, all on the terms and conditions
contained herein.

         C. Unless otherwise expressly provided herein, capitalized terms used
herein shall have the meanings as designated in the Lease.

                                   AGREEMENT:

         In consideration of the sum of Ten Dollars ($10.00), the mutual
covenants and agreements contained herein and in the Lease, and for other good
and valuable consideration, the receipt and sufficiency of which are hereby
acknowledged, Landlord and Tenant hereby agree as follows:

         1. Addition of Expansion Space to Premises. Effective as of April 1,
1999 (the "Effective Date"), the Expansion Space is hereby added to the
Premises. As of the Effective Date, all references in the Lease to the Premises
shall be deemed to include the Expansion Space. The Expansion Space shall be
added to the Premises, for all purposes, as of the Effective Date and for the
balance of the Term (as the same may be extended pursuant to the provisions of
the Lease), upon and subject to all of the terms, covenants and conditions of
the Lease.

         2. Expansion Space Delivery and Acceptance.

         (a) Delivery of Expansion Space. On or before the Effective Date,
Landlord shall deliver the Expansion Space to Tenant in its then current "as is"
condition. Notwithstanding the foregoing, in the event that Landlord is unable
to deliver the Expansion Space to Tenant by the Effective Date, regardless of
the reason therefor,



                                       A-1
<PAGE>   15


Landlord shall not be liable for any claims, damages or liabilities by reason
thereof, nor shall such circumstances make the Lease or this First Amendment
void or voidable, and Tenant's sole and exclusive remedy for such delay shall be
a postponement of Tenant's obligation to pay Rent and Additional Rent for the
Expansion Space; provided, however, that if Landlord is unable to deliver the
Expansion Space to Tenant on or before the Effective Date due to a delay caused
by Tenant or for any other cause related to Tenant's acts or omissions, Tenant's
rental obligations under the Lease as amended hereby with respect to the
Expansion Space shall begin on the Effective Date.

         (b) Tenant's Acceptance of Expansion Space and Obligation to Pay Rent.
Tenant agrees to accept the Expansion Space in its "as is" condition, and
acknowledges that Landlord makes no representations or warranties whatsoever
with respect thereto. Notwithstanding any other provision contained in the Lease
or this First Amendment, except as provided in subparagraph 2(a), Tenant agrees
that its obligation to pay Rent and Additional Rent with respect to the
Expansion Space shall commence on the Effective Date.

         3. Rent - Expansion Space. Commencing on the Effective Date, and
continuing through the Initial Term, the annual Rent due and payable for each
rentable square foot contained in the Expansion Space (in addition to any other
Rent payable pursuant to the terms of the Lease), shall be $17.00, payable in
equal monthly installments of $5,568.92. The Rent for the Expansion Space set
forth herein shall be deemed to include rental for the office furniture
identified on Exhibit B attached hereto and incorporated herein by this
reference. In the event that the Initial Term of the Lease is extended pursuant
to Paragraph 5(b), of the Lease, Rent for the Expansion Space for any extension
term of the Lease shall be increased in the same manner as provided in Exhibit B
to the Lease. In addition, Tenant shall pay to Landlord all Additional Rent
attributable to the Expansion Space, in accordance with the terms and provisions
of Paragraph 8(b) of the Lease. All rental shall be payable in accordance with
the terms and provisions of the Lease.

         4. Payment for Fire Exit and Security Camera. Landlord agrees to
install a separate fire exit with security camera (the "Fire Exit") at a
location on the Premises to be determined by Landlord. The Fire Exit shall be
installed in a good and workerlike manner and, subject to Landlord's right to
partial reimbursement by Tenant as provided in this paragraph, at Landlord's
cost and expense, but otherwise at such time and in such manner as Landlord
shall determine in its sole discretion. Tenant agrees to reimburse Landlord for
fifty percent (50%) of Landlord's costs and expenses related to the construction
and installation of the Fire Exit (the "Fire Exit Payment"). Landlord shall
notify Tenant of the cost of the Fire Exit and the amount of the Fire Exit
Payment as soon as reasonably practicable after it is known, and Tenant shall
make the Fire Exit Payment to Landlord on or before the Effective Date. In the
event that Landlord has not notified Tenant of the amount of the Fire Exit
Payment by the Effective Date, Tenant shall pay the amount of $1,750.00, which
the parties agree is one-half of the estimated cost of the Fire Exit (the
"Estimated Fire Exit Payment"), and at such time that the exact cost of the Fire
Exit is calculated, Landlord shall notify Tenant of such cost and the
corresponding Fire Exit Payment. If the Estimated Fire Exit Payment is less than
the actual Fire Exit




                                       A-2
<PAGE>   16


Payment, Tenant shall pay the difference within fifteen (15) days after receipt
of such notice, and if the Estimated Fire Exit Payment is greater than the
actual Fire Exit Payment, Tenant shall receive a corresponding credit of Rent
for the difference. All payments to be made by Tenant pursuant to the provisions
of this Paragraph 4 shall be deemed to be Additional Rent pursuant to the terms
of the Lease, and Tenant's failure to make any payment as required herein shall
constitute an event of default by Tenant under the Lease.

         5. Removal of Cabling. Prior to the Effective Date, Tenant shall
disconnect, at the Amgen VDER room, any and all fiber and copper cables that
lead from the VDER room to the Expansion Space (the "Cabling"). Tenant shall
pull the Cabling back to the Expansion Space and remove it from the cable trays
at that point. The disconnection and removal of the Cabling shall be conducted
at Tenant's sole cost and expense, in a good and workerlike manner acceptable to
Amgen, and otherwise in accordance with the provisions of the Lease, including
but not limited to Paragraph 10(c) thereof. Tenant may retain and use the
Cabling.

         6. Parking:. As of the Effective Date, Tenant shall have the right to
use eight (8) additional parking spaces in the general parking area of the Amgen
Complex as assigned by Amgen. All of the other terms of the Lease applicable to
Tenant's parking rights shall be applicable to Tenant's parking rights provided
in this Paragraph 6. The parking rights provided in this Paragraph 6 are in
addition to any other parking rights provided in the Lease.

         7. Binding Effect. Except as modified by this First Amendment, the
terms and provisions of the Lease shall remain in full force and effect, and
shall be binding upon the parties hereto, their successors and permitted
assigns. This First Amendment shall become effective only after the full
execution and delivery hereof by Landlord and Tenant.

         8. Conflict. In the event of any conflict between the provisions of
this First Amendment and the provisions of the other portions of the Lease, the
provisions of this First Amendment shall control.

         9. Ratification of Lease. All of the terms and provisions of the Lease,
as herein amended and supplemented, are hereby ratified and confirmed, and shall
remain in fall force and effect.

         10. Time is of the Essence. Time is of the essence with regard to this
First Amendment.







                                       A-3
<PAGE>   17




LANDLORD:                                 TENANT
AMGEN INC., a Delaware corporation        ARRAY BIOPHARMA INC., a Delaware
                                          corporation


By:                                       By:
   --------------------------------          ----------------------------------
Name:                                     Name: David Snitman

Title:                                    Title: COO




                                       A-4
<PAGE>   18


                                    EXHIBIT B
                              (Expansion Schedule)
<TABLE>
<CAPTION>
   EXPANSION DATE
   (DATE BY WHICH
   SUBTENANT MUST
  OCCUPY EXPANSION       BUILDING      CHANGE IN                                                      PREMISES'
       SPACE)               NO.            SF                      COMMENTS                         CUMULATIVE SF
  ----------------       --------      ---------                   --------                         -------------
<S>                      <C>           <C>          <C>                                             <C>

   April 15, 2001         Bridge         (2,650)    Western portion of the Bridge deleted from         27,125
                                                    Premises, as shown by honey-combed markings
                                                    on Exhibit B-1

   April 15, 2001           4            31,960     Expansion Space "A" shown by cross-hatching        59,085
                                                    on Exhibit B-2. Plus remainder of 3rd floor
                                                    shown as area WITHOUT cross-hatching on
                                                    Exhibit B-3.

    May 1, 2004             4             8,975     Expansion Space "B" shown by honey-combed          68,060
                                                    markings on Exhibit B-2. Subtenant may elect
                                                    to take Expansion Space at any time between
                                                    May 1, 2002 and May 1, 2004.

    May 1, 2004           3 and          49,561     Expansion Space "C". Subtenant may elect to       117,621
                          Bridge                    take Expansion Space at any time between
                                                    July 1, 2003 and May 1, 2004.

    May 1, 2004             2             9,000     Expansion Space "D" shown by cross-hatching       126,621
                                                    on Exhibit B-4. Subtenant may elect to take
                                                    Expansion Space at any time between July 1,
                                                    2002 and May 1, 2004.

    May 1, 2004             2            17,279     Expansion Space "E" shown as area WITHOUT         143,900
                                                    cross-hatching on Exhibit B-4. Subtenant may
                                                    elect to take Expansion Space at any time
                                                    between July 1, 2003 and May 1, 2004.
   Total Additional
    Square Footage                      114,125
</TABLE>




                                      B-1
<PAGE>   19


                                    EXHIBIT C
                            (Current Expansion Space)

               SEE CROSS-HATCHED AREA ON EXHIBIT C ATTACHED HERETO







                                       C-1