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                                                                  EXHIBIT 10.21A

                       FIRST AMENDMENT TO LEASE AGREEMENT


         The FIRST AMENDMENT TO LEASE AGREEMENT (this "Amendment") effective as
of February 10, 1998, by and between SN Properties Inc., a Delaware corporation
having an address of 2450 Bayshore Parkway, Mountain View, California 94043
("Landlord"), and Guilford Pharmaceuticals Inc., a Delaware corporation having
an address of 6611 Tributary Street, Baltimore, Maryland 21223 ("Tenant").

                                   BACKGROUND

         A.  Landlord and Tenant previously entered into a Lease Agreement (the
"Lease") dated June 9, 1997 concerning certain space within the building at
6200 Freeport Centre, Baltimore, Maryland.

         B.  Tenant has previously exercised its option to extend the term of
the Lease so that it would expire on June 30, 1999.

         C.  The parties hereto desire to amend the Lease to increase the space
leased to Tenant, further extend the term of the Lease, and modify the rent as
set forth herein and otherwise to clarify certain matters between them.

         THE PARTIES AGREE HEREBY AS FOLLOWS:

         1.  Definitions.  Except as specifically defined herein, capitalized
terms shall have the definition given to them in the Lease.

         2.  Amendment of Premises.  Effective February 10, 1998, the
definition of Premises in subparagraph (b) of Section I of the Lease is hereby
amended so that the Premises consist of approximately thirty-two thousand seven
hundred eight (32,708) square feet (the "Premises Square Footage") has
described Article 2 below.  Exhibit B of the Lease is amended to be as set
forth in Addendum A to this Amendment.  Landlord agrees that, in order for
Tenant to make its leased space secure from other tenants of Landlord in the
remainder of the Building, Tenant may, so long as fire and safety codes permit
it, secure the door in hallway near room 123 so that other tenants in the
building cannot enter Tenant's space and that Tenant may at Tenant's expense
add a similar door in the hallway between rooms 171 and 182.  The location of
the doors are indicated on Addendum A. Tenant agrees that Landlord shall not be
obligated to provide air conditioning or heating to rooms 182, 184, 184A, 190,
190A and192 as shown on Addendum A until such time as the remaining space
serviced by the air handler serving such rooms has been leased by Landlord to
another tenant.

         3.  Base Rent.  The parties agree that the first paragraph of
subparagraph (e) of Section I of the Lease is hereby amended to read in its
entirety as follows:

                          (e) Base Rent.  During each month of the Lease after
                          the date of this
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                          Amendment, Tenant shall pay the Base Rent which is
                          Two Dollars and Twenty-five Cents ($2.25) multiplied
                          by the Premises Square Footage of the Premises (i.e.
                          $73,593 per month).  Rent for February, 1998, shall
                          be $61,778.80 reflecting proration for 10 days in the
                          original space and 18 days in the expanded space at
                          the revised rent.

         4.  Lease Term.  The parties agree that Section III of the Lease is
hereby amended so that the term of the Lease shall now extend until midnight on
July 31, 1999 as to the entire space included in the Premises following this
Amendment.

         5.  Lease Condition of Premises.  Tenant has inspected the new areas
being added to the Premises and requested that Landlord address the items
listed on Addendum B.  Landlord agrees to address all items on Addendum B in a
timely manner.  In particular, the air handling systems and hoods will be
energized so that the hoods may be checked prior to February 10 and the
flooring and steel plate in the scale-up lab will be repaired prior to February
10.

         6.  Miscellaneous.  Except as otherwise modified by this Amendment,
the parties agree that the Lease continues in full force and effect.  Landlord
and Tenant expressly agree that neither has made any representation or promise
with respect to the Premises or the Building except as set forth in the Lease
or in the Amendment.  This Amendment contains the entire agreement of the
parties with respect to the subject matter of this Amendment and supersedes all
prior agreements, negotiations, understandings, or discussions between the
parties.  This Amendment shall be governed by the laws of the jurisdiction in
which the Building is located.

IN WITNESS WHEREOF, Landlord and Tenant have executed this Amendment as of the
day and year first written above.

Landlord:                                 Tenant:

SN PROPERTIES INC.                        GUILFORD PHARMACEUTICALS INC.

By: /s/ John H. Newman                    By: /s/ John P. Brennan
   --------------------------                ----------------------------------
         John H. Newman                            John P. Brennan
         Vice President                            Vice President, Operations

Attachments:     Addendum A -- Floor plan indicating leased premises and common
                 area after the Amendment.
                 Addendum B -- Repair items