WITNESSETH

Exhibit 10.4a
Fifth Amendment to Lease between LJL BioSystems, Inc. and The Xxx Xxxxxxx
1989 Revocable Trust

                            FIFTH AMENDMENT TO LEASE

This amendment to lease ("Fifth Amendment") is made this 7th day of December
1999, by and between The Xxx Xxxxxxx 1989 Revocable Trust, having an address at
00000 Xxxxx Xx Xxxx Xxxxxxxxx, Xxxxx 000, Xxxxxxxxx, Xxxxxxxxxx 00000
("Landlord") and LJL BioSystems, a Delaware corporation having its principal
place of business at 000 Xxxxxx Xxxxx, Xxxxxxxxx, Xxxxxxxxxx, 00000 ("Tenant").

                                   WITNESSETH

WHEREAS Landlord and Tenant entered into a lease dated October 14, 1992, and
subsequent lease amendments dated December 3, 1993, October 20, 1995, September
16, 1996, and June 10, 1999 (collectively the "Lease") for the premises located
at 000 Xxxxxx Xxxxx in Sunnyvale, California ("Premises"); and

WHEREAS effective the date of this Fifth Amendment, Landlord and Tenant wish to
modify the Lease to (i) change the expiration date of the Lease; and (ii) define
the monthly rent for the months of February through April, 2000;

NOW, THEREFORE, in order to effect the intent of the parties as set forth above
and for good and valuable consideration exchanged between the parties, the Lease
is amended as follows:

1.       The Lease expiration date is changed from April 30, 2000 to December
         31, 2002.

2.       Monthly rent from May 1, 2000 through December 31, 2002 shall be
         payable according to the following schedule:
         May 1, 2000 through January 31, 2001:          $18,736.00 per month
         February 1, 2001 through January 31, 2002:     $19,313.00 per month
         February 1, 2002 through December 31, 2002:    $19,889.00 per month

3.       All defined terms shall have the same meanings as in the Lease, except
         as otherwise stated in this Fifth Amendment. In the event of any
         conflict or inconsistency between the terms and provisions of this
         Fifth Amendment and the terms and provisions of the Lease, the terms
         and provisions of this Fifth Amendment shall prevail.

IN WITNESS WHEREOF, the parties hereto have set its hands to this Fifth
Amendment as of the day and date first above written.

LANDLORD                                 TENANT

Xxx Xxxxxxx 1989 Revocable Trust         LJL BioSystems, a Delaware Corporation

By: /s/ XXXX X. XXXXXXX                  By: /s/ XXXXXX X. XXXXX
   --------------------                     --------------------
Its: General Partner                     Its: Vice President, Finance and
                                              Administration


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