PROMISSORY NOTE

$2,000,000                                                     January [ ], 2005
                                                          Pleasanton, California

      FOR VALUE RECEIVED, Calypte Biomedical Corporation, a Delaware corporation
(the "Borrower") promises to pay to the order of Marr Technologies, B.V. ("MTBV"
or the "Payee"),  the  principal  amount of Two Million  United  States  Dollars
($2,000,000.00)  ("Principal").  The unpaid  Principal due under this Note shall
bear interest from the date hereof until paid,  computed at a rate equivalent of
7.00%  per  annum  (computed  on the basis of a  360-day  year and  actual  days
elapsed).  Any amount of Principal  or interest  which is unpaid on its due date
shall bear  interest  from the due date until  payment  (as well after as before
judgment) at a rate of 9.00% per annum.

      The  Principal  of this Note shall be payable in full upon the  earlier of
(i) the closing of [ ] on terms  substantially  equivalent to those described in
the Senior  Convertible  Note Term Sheet attached  hereto as Exhibit A, in which
MTBV shall participate in an investment amount of at least $2,000,000,  or, (ii)
31 March 2005 (the "Maturity  Date").  All accrued interest on the entire unpaid
principal shall likewise be due on the Maturity Date.

      Payment of the Principal and interest shall be made in lawful money of the
United States in the form of a wire transfer of immediately  available  funds to
an account  specified  by Payee or at such other place as Payee may from time to
time direct in writing.  Should the Maturity  Date be determined on the basis of
alternative (i) as described in the immediately preceding paragraph, Payee shall
not be repaid the  Principal on the  Maturity  Date but the  Principal  shall be
regarded  as having  been  invested  by Payee in the first  tranche of the above
mentioned financing.

      No delay on the part of the Payee in exercising any right under this Note,
or other  undertaking  securing or affecting this Note shall operate as a waiver
of such right or any other right, nor shall any omission in exercising any right
on the part of the Payee  under  this  Note.  In the event this Note is not paid
when due, the Borrower  shall pay all costs of  collection,  including,  without
limitation, reasonable attorneys' fees.

      All notices  and other  communications  hereunder  shall be in writing and
shall be deemed  received  (1) upon  receipt or refusal  thereof,  if  delivered
personally or via overnight  courier service,  or (2) upon receipt by the sender
of transmission confirmation, if delivered via facsimile. Notice to either party
hereto, if faxed or sent by overnight courier service, shall be to the following
addresses:

<PAGE>

      If to the Payee, to:                   If to the Borrower, to:

      Marr Technologies, BV                  Calypte Biomedical Corporation
      Strawinskylaan 1431                    5000 Hopyard Road, Suite 480
      1077XX Amsterdam                       Pleasanton, CA 94588
      Netherlands                            Attention: Executive Vice President
                                                and CFO
      Attention:  Christian Strik            Facsimile:  925-730-0146
      Facsimile:

Any party may change their address for notice by giving all other parties notice
of such change pursuant to this paragraph.

      At the option of the  Borrower,  all or any portion of the  Principal  and
accrued  interest due on this Note may be otherwise  prepaid  without premium or
penalty,  the amount of the  prepayment to be applied first to accrued  interest
and the remainder to any unpaid balance of Principal.

      This Note and the rights and  obligations  of the parties  hereto shall be
governed by and construed in accordance  with the laws of the State of Delaware,
without regard to the conflicts of laws principles of the State of Delaware. All
rights of Payee  hereunder  shall  inure to the  benefit of its  successors  and
assigns,  and all  obligations  of the Borrower  shall bind its  successors  and
assigns;  provided,  however,  that  this  Note and the  Borrower's  obligations
hereunder  shall not be  assignable  by the Borrower  without the prior  written
consent of Payee.  The Borrower  hereby  waives  presentment,  demand,  protest,
notice of dishonor  and/or  protest,  notice of nonpayment and all other notices
and demands, and assents to the extension of the time of payment, forbearance or
other indulgence, without notice.

      To induce Payee to accept this Note, the Borrower irrevocably agrees that,
subject to Payee's sole and absolute  election,  all actions or proceedings,  in
any way, manner or respect, arising out of or from or related to this Note shall
be litigated in courts  having  situs  within the City of  Wilmington,  State of
Delaware.  The Borrower hereby  consents and submits to the  jurisdiction of any
local,  state or federal court located within said City and State.  The Borrower
hereby  waives  any right it may have to  transfer  or  change  the venue of any
litigation  brought  against  the  Borrower  by Payee in  accordance  with  this
paragraph,  and the Borrower hereby  specifically waives any right to assert the
doctrine of forum non conveniens.

      THE BORROWER  IRREVOCABLY WAIVES ANY RIGHT TO TRIAL BY JURY IN ANY ACTION,
SUIT,  COUNTERCLAIM,  OR PROCEEDING (I) TO ENFORCE OR DEFEND ANY RIGHTS UNDER OR
IN CONNECTION WITH THIS NOTE OR ANY AMENDMENT, INSTRUMENT, DOCUMENT OR AGREEMENT
DELIVERED  OR WHICH MAY IN THE FUTURE BE DELIVERED IN  CONNECTION  HEREWITH,  OR
(II) ARISING FROM ANY DISPUTE OR  CONTROVERSY  IN CONNECTION  WITH OR RELATED TO
THIS NOTE OR ANY SUCH AMENDMENT,  INSTRUMENT,  DOCUMENT OR AGREEMENT, AND AGREES
THAT ANY SUCH ACTION,  SUIT  COUNTERCLAIM OR PROCEEDING  SHALL BE TRIED BEFORE A
COURT AND NOT BEFORE A JURY.

                                      -2-
<PAGE>

      All of Payee's  rights and  remedies  under this Note are  cumulative  and
non-exclusive.  The  acceptance by Payee of any partial  payment made  hereunder
after the time when any of the  Borrower's  liabilities  become due and  payable
will not  establish  a custom or waive any  rights  of Payee to  enforce  prompt
payment hereof. Payee's failure to require strict performance by the Borrower of
any  provision  of this Note shall not waive,  affect or  diminish  any right of
Payee thereafter to remain in strict compliance and performance herewith.

      IN WITNESS  WHEREOF,  Calypte  Biomedical  Corporation  has  executed  and
delivered this Promissory Note the day and year first written above.

                                         CALYPTE BIOMEDICAL CORPORATION


                                           By:
                                              --------------------------------
                                              Richard D. Brounstein
                                              Executive Vice President
                                                    and Chief Financial Officer

                                      -3-
<PAGE>

                          AMENDMENT TO PROMISSORY NOTE

      THIS AMENDMENT to Promissory  Note (this  "Amendment") is made as of March
30, 2005, by and between Calypte Biomedical Corporation,  a Delaware corporation
(the "Borrower"),  and Marr Technologies,  B.V. ("MTBV" or the "Payee").  Unless
otherwise  defined  herein,  all  capitalized  terms used herein  shall have the
meanings given to them in the Promissory Note referred to below.

      WHEREAS, the Borrower and the Payee are parties to a Promissory Note dated
January 14, 2005 (the "Promissory Note");

      WHEREAS,  pursuant to the terms of the Promissory  Note, the Maturity Date
is now 31 March 2005;

      WHEREAS,  subsequent to the execution of the Promissory Note, the terms of
the financing changed from those set forth on Term Sheet;

      WHEREAS,  the parties  desire to amend and modify the  Promissory  Note to
change  the  definition  of  Maturity  Date to extend the  outside  due date for
payment of the Promissory Note.

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

1. The second paragraph of the Promissory Note is hereby amended and restated to
read in its entirety as follows:

      "The  Principal  of this Note shall be payable in full upon the earlier of
(i) the  closing  of an 8%  Convertible  Note  financing  in  which  MTBV  shall
participate  in an investment  amount of at least  $2,000,000,  or (ii) 30 April
2005 (the "Maturity Date").  All accrued interest on the entire unpaid principal
shall likewise be due on the Maturity Date."

2. Except for the  amendments  provided for herein,  the  Promissory  Note shall
remain unchanged and in full force and effect.

3. This Amendment may be executed in separate counterparts,  each of which shall
be deemed to be an original,  but each of which  together  shall be deemed to be
one and the same instrument.

4. This Amendment shall be governed by and construed in accordance with the laws
of  the  State  of  Delaware  without  giving  effect  to the  conflicts  of law
principles thereof.

      IN WITNESS WHEREOF, each of the parties hereto has caused a counterpart of
this  Amendment  to be duly  executed  and  delivered as of the date first above
written.


                             CALYPTE BIOMEDICAL CORPORATION

                             By:
                                -----------------------------
                                Richard D. Brounstein, Executive Vice President
                                and Chief Financial Officer


                             MARR TECHNOLOGIES, BV

                             By:
                                -----------------------------