Document:

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                                    SUBLEASE

                  SUBLEASE ("SUBLEASE") dated as of December 17, 1998, by and
between CAMBRIDGE BIOTECH CORPORATION, the address of which is c/o bioMerieux,
Inc., 595 Anglum Drive, St. Louis, Missouri 63042-2395 ("SUBLESSOR"), and
CALYPTE BIOMEDICAL CORPORATION, the address of which is 1440 Fourth Street,
Berkeley, California 94710 ("SUBLESSEE").

                                   WITNESSETH:

                  WHEREAS, Sublessor is the sublessee of DynCorp (lessee under a
certain Lease between W.M. Rickman Construction Company, as Landlord, and
Sublessor, as subtenant, relating to the leased premises), pursuant to a
Sublease Agreement dated April 6, 1995 (as amended through the date hereof the
"Master Lease"; capitalized terms used and not otherwise defined herein have the
respective meanings given them in the Master Lease);

                  WHEREAS, Sublessor has sold to Sublessee, pursuant to the
Asset Acquisition Agreement between the Sublessor and the Sublessee dated
November 18, 1998 (the "Acquisition Agreement"), the Acquired Assets (as defined
in the Acquisition Agreement) located in part on the leased premises; and

                  WHEREAS, Sublessor now wishes to sublease to Sublessee, and
Sublessee wishes to sublease from Sublessor, the leased premises on the
following terms and conditions;

                  NOW, THEREFORE, Sublessor and Sublessee hereby agree as
follows:

                                    ARTICLE I

1.       SUBLEASE. Upon and subject to the terms and conditions hereinafter set
forth, and subject to the terms and conditions of the Master Lease, Sublessor
subleases to Sublessee the leased premises.

2.       TERM. The term of this Sublease shall commence on December 11, 1998 and
end on March 30, 2000, or prior to such date upon one hundred eighty (180) days
prior written notice delivered by Sublessee.

3.       RENT. The rent hereunder shall equal the rent and the additional rent
as provided in the Master Lease.

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                                   ARTICLE II

1.       SUBORDINATION TO MASTER LEASE. This Sublease is and shall at all times
be subject and subordinate to the Master Lease, and notwithstanding anything
elsewhere herein to the contrary, upon the expiration or earlier termination of
the Master Lease this Sublease shall automatically and simultaneously terminate.

2.       INCORPORATION OF TERMS OF MASTER LEASE. In addition to the terms and
conditions set forth herein, and except as expressly modified herein, the terms,
conditions and respective obligations of Sublessor and Sublessee to each other
under this Sublease shall be the terms, conditions and respective obligations of
"Lessee" and "Sublessee" to each other under the Master Lease, which terms,
conditions and obligations are hereby incorporated herein. Therefore, for
purposes of this Sublease, wherever in the Master Lease the word "Lessee" is
used, it shall be deemed to mean and refer to the Sublessor herein, wherever in
the Master Lease the word "Sublessee" is used, it shall be deemed to mean and
refer to the Sublessee herein.

3.       ASSUMPTION BY SUBLESSEE. During the term of this Sublease, and
thereafter with respect to obligations which have arisen prior to the
termination or expiration of the term of this Sublease, Sublessee expressly
assumes and agrees to pay, perform and comply with for the benefit of Sublessor
and the Lessor under the Master Lease each and every payment and performance
obligation under the Master Lease with respect to Sublessee and the subleased
property.

4.       ENVIRONMENTAL LIABILITIES.

a.       Notwithstanding any other provision of this Sublease, Sublessor shall
indemnify and hold harmless the Sublessee and Sublessee's officers, directors,
employees, agents, affiliates, successors and assigns from and against, any and
all losses, liabilities, damages, costs and expenses (including reasonable fees
and disbursements of counsel and expenses of investigation and defense), claims,
or other obligations of any nature to the extent attributable to (a)
environmental conditions existing at the leased premises prior to the execution
of this Sublease which are attributable to the actions of Sublessor while
Sublessor occupied the leased premises (or are actually known to the officers of
Sublessor), (b) any violation of environmental laws based on actions, failures
to act, or conditions associated with the leased premises during the time that
Sublessor occupied the leased premises, or (c) environmental conditions existing
at the leased premises prior to the execution of this Sublease which are not
attributable to the actions of Sublessor while Sublessor occupied the leased
premises, to the extent that indemnification therefor is paid to the Sublessor
pursuant to existing agreements with Aquila Biopharmaceutical Corporation (which
indemnification shall be sought if applicable in good faith by the Sublessor),
or (d) any violation of environmental laws based on actions, failures to act, or
conditions not associated with the leased premises during the time that
Sublessor occupied the leased premises, to the extent that indemnification
therefor is paid to the Sublessor pursuant to existing agreements with Aquila
Biopharmaceutical Corporation (which indemnification shall be so sought).

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b.       Notwithstanding any other provision of this Sublease, Sublessee shall
indemnify and hold harmless Sublessor and Sublessor's officers, directors,
employees, agents, affiliates, successors and assigns from and against, any and
all losses, liabilities, damages, costs and expenses (including reasonable fees
and disbursements of counsel and expenses of investigation and defense), claims,
or other obligations to the extent attributable to (a) environmental conditions
which are the result of actions of the Sublessee subsequent to the execution of
this Sublease, or (b) any violation of environmental laws based on actions,
failures to act, or conditions associated with the leased premises during the
Sublessee's occupation of the leased premises.

5.       DEFAULT. Any default under the Master Lease shall constitute a default
under this Sublease, and upon the occurrence of any default under the Master
Lease, Sublessor shall have with respect to Sublessee and the subleased property
all of the remedies afforded the Lessor with respect to the Lessee and the
leased property under the Master Lease.

6.       NOTICES. Except as required by law for the posting of notices, all
notices, requests, demands and other communications hereunder must be in writing
and shall be personally served or mailed (by registered or certified mail,
return receipt requested and postage prepaid), or delivered by a national
overnight delivery service such as Federal Express or D.H.L., or by facsimile
transmission addressed to the respective parties, as follows:

         (a) if to Sublessor:

         Cambridge Biotech Corporation
         595 Anglum Drive
         St. Louis, Missouri 63042-2395
         Attention: President
         Telecopier: (314) 731-7319

             if to Sublessee:

         Calypte Biomedical Corporation
         1140 [sic] Fourth Street
         Berkeley, California 94710
         Attention: President
         Telecopier: (510) 526-538l

         Any such mailing, delivery or other permitted service shall be deemed
to be complete on the day of the confirmed receipt or refusal thereof.

                                      -3-
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7.       MISCELLANEOUS.

a.       SURVIVAL, CHOICE OF LAW. Anything contained in this Sublease to the
contrary notwithstanding, all claims against, and liabilities of, Sublessee or
Sublessor arising prior to any date of termination of this Sublease shall
survive such termination. If any late charges provided for in any provision of
this Sublease are based upon a rate in excess of the maximum rate permitted by
applicable law, the parties agree that such charges shall be fixed at the
maximum permissible rate. All the terms and provisions of this Sublease shall be
binding upon and inure to the benefit of the parties hereto and their respective
successors and assigns. The headings in this Sublease are for convenience of
reference only and shall not limit or otherwise affect the meaning hereof. This
Sublease shall be governed by and construed in accordance with the laws of
Maryland, except as to matters which under the laws of a State, or under
applicable procedural conflicts of laws rules, require the application of laws
of the State.

b.       COUNTERPARTS. This Sublease may be executed in separate counterparts,
each of which shall be considered as original when each party has executed and
delivered to the other one or more copies of this Sublease.

c.       ENTIRE AGREEMENT. There are no oral or written agreements or
representations between the parties hereto affecting this Sublease. This
Sublease supersedes and cancels any and all previous negotiations, arrangements,
representations, brochures, agreements and understandings, if any, between
Sublessor and Sublessee.

d.       AMENDMENTS IN WRITING. Neither this Sublease nor any provision hereof
may be changed, waived, discharged or terminated except by an instrument in
writing signed by Sublessor and Sublessee

e.       SEVERABILITY. If any provision of this Sublease or the application of
such provision to any person, entity or circumstance is found invalid or
unenforceable by a court of competent jurisdiction, such determination shall
not affect the other provisions of this Sublease and all other provisions of
this Sublease shall be deemed valid and enforceable.

f.       SUCCESSORS. All rights and obligations of Sublessor and Sublessee under
this Sublease shall extend to and bind the respective heirs, executors
administrators and the permitted concessionaires, successors, subtenants and
assignees of the parties.

                                      -4-
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                  IN WITNESS WHEREOF, the parties have executed this Sublease by
their duly authorized signing officers.

                                        CAMBRIDGE BIOTECH CORPORATION

                                        By:  /s/ Philippe Sans
                                           -------------------------------------
                                        Name: Philippe Sans
                                        Title:   President

                                        CALYPTE BIOMEDICAL CORPORATION

                                        By:  /s/ William A. Boeger III
                                           -------------------------------------
                                        Name: William A. Boeger III
                                              Title: Chief Executive Officer

                                      -5-<PAGE>

                            LEASE EXTENSION AGREEMENT

This agreement is dated October 12, 1999 for reference purposes and is an
additional modification to the current Lease dated November 30, 1990 between
Charles A. Grant and Mark Greenberg (LESSOR) and Urnotech Calypte Biomedical
Corporation (LESSEE) for the property known as 1440 Fourth Street, Berkeley,
California:

1) LEASE EXTENDED THROUGH AUGUST 2000. The Lease is hereby extended five months
through August 31, 2000. The lease rate for this extension period will remain
$27,000 per month.

2) HOLDING OVER. If LESSEE remains in possession of the premises per Paragraph
26 (Holding Over), then the agreed monthly rent is $29,000.

SIGNED:     /s/  Charles A. Grant        G.P.                10/12/99
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           FOR LESSOR                   TITLE                 DATE

SIGNED:     /s/  Nancy E. Katz        President             10/28/99
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           FOR LESSOR                   TITLE                 DATE

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