Document:

<PAGE>
                                                                     Exhibit 4.1

                         CALYPTE BIOMEDICAL CORPORATION

                                  COMMON STOCK

                               PURCHASE AGREEMENT

                                 MARCH 2, 2000

<PAGE>

NOTICE TO PURCHASERS IN ALL STATES:

IN MAKING AN INVESTMENT DECISION INVESTORS MUST RELY ON THEIR OWN EXAMINATION OF
THE ISSUER AND THE TERMS OF THE OFFERING, INCLUDING THE MERITS AND RISKS
INVOLVED. THESE SECURITIES HAVE NOT BEEN RECOMMENDED BY ANY FEDERAL OR STATE
SECURITIES COMMISSION OR REGULATORY AUTHORITY. FURTHERMORE, THE FOREGOING
AUTHORITIES HAVE NOT CONFIRMED THE ACCURACY OR DETERMINED THE ADEQUACY OF THIS
DOCUMENT. ANY REPRESENTATION TO THE CONTRARY IS A CRIMINAL OFFENSE.

THESE SECURITIES ARE SUBJECT TO RESTRICTIONS ON TRANSFERABILITY AND RESALE AND
MAY NOT BE TRANSFERRED OR RESOLD EXCEPT AS PERMITTED UNDER THE SECURITIES ACT OF
1933, AS AMENDED, AND THE APPLICABLE STATE SECURITIES LAWS, PURSUANT TO
REGISTRATION OR EXEMPTION THEREFROM. INVESTORS SHOULD BE AWARE THAT THEY WILL BE
REQUIRED TO BEAR THE FINANCIAL RISKS OF THIS INVESTMENT FOR AN INDEFINITE PERIOD
OF TIME.

<PAGE>

                                  COMMON STOCK

                               PURCHASE AGREEMENT

         This Agreement ("Agreement") is made as of March 2, 2000 (the
"Execution Date"), by and among Calypte Biomedical Corporation, a Delaware
corporation (the "Company"), and each of those persons and entities, severally
and not jointly, listed as a Purchaser on the Schedule of Purchasers attached as
Exhibit A hereto. Such persons and entities are hereinafter collectively
referred to herein as "Purchasers" and each individually as a "Purchaser."

                                   AGREEMENT

         In consideration of the mutual covenants contained in this Agreement,
and for other good and valuable consideration, the receipt of which is hereby
acknowledged, the Company and each Purchaser (severally and not jointly) hereby
agree as follows:

         SECTION 1. AUTHORIZATION OF SALE OF THE SECURITIES.

         Subject to the terms and conditions of this Agreement, the Company has,
or before the Closing (as defined below) will have, authorized the sale and
issuance of up to 4,096,000 shares of its Common Stock (the "Common Stock"). The
shares of Common Stock sold hereunder shall be referred to herein as the
"Shares" or the "Securities."

         SECTION 2. AGREEMENT TO SELL AND PURCHASE THE SECURITIES.

         2.1      SALE OF SHARES. At the Closing (as defined in Section 3),
the Company will sell to each Purchaser, and each Purchaser will purchase
from the Company, at a purchase price of Two Dollars and Five Cents ($2.05)
per Share, the number of Shares set forth next to such Purchaser's name on
the Schedule of Purchasers attached hereto as Exhibit A (the "Schedule of
Purchasers").

         2.2      SEPARATE AGREEMENT. Each Purchaser shall severally, and not
jointly, be liable for only the purchase of the Shares that appear on Exhibit
A hereto and that relate to such Purchaser. The Company's agreement with each
of the Purchasers is a separate agreement, and the sale of Shares to each of
the Purchasers is a separate sale. The obligations of each Purchaser
hereunder are expressly not conditioned on the purchase by any or all of the
other Purchasers of the Shares such other Purchasers have agreed to purchase.

         SECTION 3. CLOSING AND DELIVERY.

         3.1      CLOSING. The Closing of the purchase and sale of the Shares
pursuant to this Agreement (the "Closing") shall be held as soon as
practicable after the effectiveness of the Registration Statement, as set
forth in Section 9.1(a) hereof, to be filed with the Securities and Exchange
Commission (the "SEC" or the "Commission"), and satisfaction or waiver of all
other conditions to Closing set forth in Sections 7 and 8 hereof, at the
offices of Heller Ehrman White & McAuliffe, 525 University Avenue, Palo Alto,
California 94301, or on such other date and place as may be agreed to by the
Company and the Purchasers.

<PAGE>

         The Company shall give at least one (1) business day prior written
notice to the Purchasers, in a manner provided for in Section 11 hereof, of the
date, time and location of the Closing. At or prior to the Closing, each
Purchaser shall execute any related agreements or other documents required to be
executed hereunder, dated as of the date of the Closing (the "Closing Date").

         3.2      DELIVERY OF THE SHARES AT THE CLOSING. At the Closing, the
Company shall deliver to each Purchaser stock certificates registered in the
name of such Purchaser, or in such nominee name(s) as designated by such
Purchaser, representing the number of shares of Common Stock to be purchased by
such Purchaser at the Closing as set forth in the Schedule of Purchasers against
payment of the purchase price for such shares. The name(s) in which the stock
certificates are to be issued to each Purchaser are set forth in the Stock
Certificate Questionnaire in the form attached hereto as Appendix I, as
completed by each Purchaser.

         SECTION 4. REPRESENTATIONS, WARRANTIES AND COVENANTS OF THE COMPANY.

         Except as set forth on the Schedule of Exceptions attached hereto as
Exhibit B, the Company hereby represents and warrants as of the date hereof to,
and covenants with, the Purchasers as follows:

         4.1      ORGANIZATION AND STANDING. The Company has been duly
incorporated and is validly existing as a corporation in good standing under the
laws of Delaware, has full corporate power and authority to own or lease its
properties and conduct its business as presently conducted, and is duly
qualified as a foreign corporation and in good standing in all jurisdictions in
which the character of the property owned or leased or the nature of the
business transacted by it makes qualification necessary (except where the
failure to be so qualified would not have a material adverse effect on the
business, properties, financial condition or results or operations of the
Company). The Company has no subsidiaries or equity interest in any other
entity.

         4.2      CORPORATE POWER; AUTHORIZATION. The Company has all requisite
corporate power, and has taken all requisite corporate action, to execute and
deliver this Agreement, sell and issue the Shares and carry out and perform all
of its obligations under this Agreement. This Agreement constitutes the legal,
valid and binding obligation of the Company, enforceable in accordance with its
terms, except (i) as limited by applicable bankruptcy, insolvency,
reorganization, moratorium or similar laws relating to or affecting the
enforcement of creditors' rights generally, (ii) as limited by equitable
principles generally, including any specific performance, and (iii) as to those
provisions of Section 9.3 relating to indemnity or contribution. The execution
and delivery of this Agreement does not, and the performance of this Agreement
and the compliance with the provisions hereof and the issuance, sale and
delivery of the Shares by the Company will not conflict with, or result in a
breach or violation of the terms, conditions or provisions of, or constitute a
default under, or result in the creation or imposition of any lien pursuant to
the terms of, the Certificate of Incorporation or Bylaws of the Company or any
statute, law, rule applicable to the Company or regulation or any state or
federal order, judgment or decree applicable to the Company or any indenture,
mortgage, lease or other agreement or

                                       2
<PAGE>

instrument to which the Company or any of its properties is subject, where such
conflict, breach or violation would have a material adverse effect on the
Company.

         4.3      ISSUANCE AND DELIVERY OF THE SHARES. The Shares, when issued
and paid for in compliance with the provisions of this Agreement, will be
validly issued, fully paid and nonassessable. The issuance and delivery of the
Shares is not subject to preemptive, co-sale, right of first refusal or any
other similar rights of the shareholders of the Company or any liens or
encumbrances. Such issuance and delivery will not cause neither an increase in
the number of shares issuable pursuant to any securities of the Company that are
outstanding as of the Execution Date nor a decrease in the exercise or
conversion price, of any such securities.

         4.4      SEC DOCUMENTS; FINANCIAL STATEMENTS. The Company has filed in
a timely manner all documents that the Company was required to file with the SEC
under Sections 13, 14(a) and 15(d) of the Securities Exchange Act of 1934, as
amended (the "Exchange Act"), during the twelve (12) months preceding the date
of this Agreement. As of their respective filing dates (or, if amended prior to
the date of this Agreement, when amended), all documents filed by the Company
with the SEC (the "SEC Documents") complied in all material respects with the
requirements of the Exchange Act. None of the SEC Documents as of their
respective dates contained any untrue statement of material fact or omitted to
state a material fact required to be stated therein or necessary to make the
statements made therein, in light of the circumstances under which they were
made, not misleading. The financial statements of the Company included in the
SEC Documents (the "Financial Statements") comply as to form in all material
respects with applicable accounting requirements and with the published rules
and regulations of the SEC with respect thereto. The Financial Statements have
been prepared in accordance with generally accepted accounting principles
consistently applied and fairly present the financial position of the Company at
the dates thereof and the results of its operations and cash flows for the
periods then ended (subject, in the case of unaudited statements, to normal,
recurring adjustments).

         4.5      INTELLECTUAL PROPERTY. Company owns or possesses adequate
rights to use all material patents, patent rights, inventions, trade secrets and
know-how described or referred to in the SEC Documents as owned or used by it or
that are necessary for the conduct of its business as presently conducted and as
described in the SEC Documents. Except as set forth in the SEC Documents, the
Company has not received any notice of, nor has any knowledge of, any
infringement of or conflict with asserted rights of others with respect to any
patent, patent right, invention, trade secret or know-how that, individually or
in the aggregate, if the subject of an unfavorable decision, ruling or finding,
would have a material adverse effect on the business, properties, financial
condition or results or operations of the Company.

         4.6      CAPITALIZATION. All of the Company's outstanding shares of
capital stock have been duly authorized and validly issued and are fully paid
and nonassessable, have been issued in compliance with all federal and state
securities laws, and were not issued in violation of or subject to any
preemptive right or other rights to subscribe for or purchase securities. The
actual authorized and outstanding capital stock of the Company as of the date
hereof is as set forth in Exhibit B. Except as set forth in Exhibit B, there are
no outstanding options to purchase, or any preemptive rights or other rights to
subscribe for or to purchase, any securities or obligations

                                       3
<PAGE>

convertible into, or any contracts or commitments to issue or sell shares of the
company's capital stock or any such options, rights, convertible securities or
obligations.

         4.7      LITIGATION. There is no pending or, to the Company's
knowledge, threatened, action, suit or other proceeding to which the Company is
a party or to which its property or assets are subject.

         4.8      GOVERNMENTAL CONSENTS. No consent, approval, order or
authorization of, or registration, qualification, designation, declaration or
filing with, any federal, state, or local governmental authority on the part of
the Company is required in connection with the consummation of the transactions
contemplated by this Agreement except for (a) compliance with the securities and
blue sky laws in the states and other jurisdictions in which shares of Common
Stock are offered and/or sold, which compliance will be effected in accordance
with such laws, and (b) the filing of a registration statement and all
amendments thereto with the SEC as contemplated by Section 9.1 of this
Agreement.

         4.9      NO MATERIAL ADVERSE CHANGE. Since September 30, 1999, there
have not been any changes in the assets, liabilities, financial condition or
operations of the Company from that reflected in the Financial Statements except
changes which have not been, either individually or in the aggregate, materially
adverse.

         4.10     LISTING; MAINTENANCE OF LISTING. The Company's Common Stock is
traded on the Nasdaq SmallCap Market. For so long as the Company is obligated to
keep in effect the Registration Statement provided for in Section 9 hereof, the
Company will use its reasonable best efforts to maintain its listing on the
Nasdaq SmallCap Market, the Nasdaq National Market or a national securities
exchange, as defined in the Exchange Act.

         SECTION 5. REPRESENTATIONS, WARRANTIES AND COVENANTS OF THE PURCHASERS.

         5.1      REPRESENTATIONS AND WARRANTIES. Each Purchaser, severally and
not jointly, represents and warrants to and covenants with the Company that:

                  (a)      Purchaser, taking into account the personnel and
resources it can practically bring to bear on the purchase of the Securities
contemplated hereby, either alone or together with the advice of such
Purchaser's purchaser representative, is knowledgeable, sophisticated and
experienced in making, and is qualified to make, decisions with respect to
investments in shares presenting an investment decision like that involved in
the purchase of the Securities, including investments in securities issued by
the Company, and has requested, received, reviewed and considered, either alone
or with such Purchaser's purchaser representative, all information Purchaser
deems relevant (including the SEC documents) in making an informed decision to
purchase the Securities.

                  (b)      Purchaser is acquiring the Securities being acquired
by Purchaser pursuant to this Agreement in the ordinary course of its business
and for its own account for investment only and with no present intention of
distributing any of such Securities or any arrangement or

                                       4
<PAGE>

understanding with any other persons regarding the distribution of such
Securities, except in compliance with Section 5.1(c).

                  (c)      Purchaser will not, directly or indirectly, offer,
sell, pledge, transfer or otherwise dispose of (or solicit any offers to buy,
purchase or otherwise acquire or take a pledge of) any of the securities
purchased hereunder except in compliance with the Securities Act of 1933, as
amended (the "Securities Act"), applicable blue sky laws, and the rules and
regulations promulgated thereunder.

                  (d)      Purchaser has completed or caused to be completed the
Stock Certificate Questionnaire and the Registration Questionnaire, attached
hereto as Appendix I and Appendix II, respectively, for use in preparation of
the Registration Statement to be filed by the Company, and the answers thereto
are true and correct as of the date hereof and will be true and correct as of
the effective date of the applicable Registration Statement (provided that
Purchaser shall be entitled to update such information by providing notice
thereof to the Company prior to the effective date of such Registration
Statement).

                  (e)      Purchaser has, in connection with its decision to
purchase the Securities, relied with respect to the Company and its affairs
solely upon the SEC Documents, the representations and warranties of the Company
contained herein and oral statements of the Company's management made at
meetings with the Purchaser.

                  (f)      Purchaser is an "accredited investor" within the
meaning of Rule 501 of Regulation D promulgated under the Securities Act or a
Qualified Institutional Buyer within the meaning of Rule 144A promulgated under
the Securities Act.

                  (g)      Purchaser has full right, power, authority and
capacity to enter into this Agreement and to consummate the transactions
contemplated hereby and has taken all necessary action to authorize the
execution, delivery and performance of this Agreement. Upon the execution and
delivery of this Agreement by Purchaser, this Agreement shall constitute a valid
and binding obligation of Purchaser, enforceable in accordance with its terms,
except (i) as limited by applicable bankruptcy, insolvency, reorganization,
moratorium or similar laws relating to or affecting the enforcement of
creditors' rights generally, (ii) as limited by equitable principles generally,
including any specific performance, and (iii) as to those provisions of Section
9.3 relating to indemnity or contribution.

         5.2      RESTRICTION ON SHORT SALES. Purchaser represents and warrants
to and covenants with the Company that Purchaser has not engaged and will not
engage in any short sales of the Company's Common Stock prior to the
effectiveness of the Registration Statement, except to the extent that any such
short sale is fully covered by shares of Common Stock of the Company other than
the Shares.

         5.3      NO ADVICE PROVIDED. Purchaser understands that nothing in this
Agreement or any other materials presented to Purchaser in connection with the
purchase and sale of the Shares constitutes legal, tax or investment advice and
that no independent legal counsel has reviewed these documents and materials on
Purchaser's behalf. Purchaser has consulted such legal, tax

                                       5
<PAGE>

and investment advisors as it, in its sole discretion, has deemed necessary or
appropriate in connection with its purchase of the Shares.

         SECTION 6. SURVIVAL OF REPRESENTATIONS, WARRANTIES AND AGREEMENTS.

         Notwithstanding any investigation made by any party to this Agreement,
all covenants, agreements, representations and warranties made by the Company
and each Purchaser herein and in the certificates for the securities delivered
pursuant hereto shall survive the execution of this Agreement, the delivery to
the Purchasers of the securities being purchased and the payment therefor.

         SECTION 7. CONDITIONS TO COMPANY'S OBLIGATIONS AT THE CLOSING.

         The Company's obligation to complete the sale and issuance of the
Securities and deliver shares of Common Stock to each Purchaser, individually,
as set forth in the Schedule of Purchasers shall be subject to the following
conditions to the extent not waived by the Company:

         7.1      RECEIPT OF PAYMENT. The Company shall have received payment,
by check or wire transfer of immediately available funds, in the full amount of
the purchase price for the number of Shares being purchased by such Purchaser at
the Closing as set forth in the Schedule of Purchasers.

         7.2      REGISTRATION STATEMENT EFFECTIVE. The Registration Statement
filed by the Company pursuant to Section 9 shall have become effective, and no
stop order suspending the effectiveness thereof shall have been issued and no
proceedings therefor shall be pending or threatened by the Securities and
Exchange Commission, ("the Commission").

         7.3      REPRESENTATIONS AND WARRANTIES CORRECT. The representations
and warranties made by such Purchaser in Section 5 hereof shall be true and
correct when made, and shall be true and correct on the Closing Date.

         SECTION 8. CONDITIONS TO PURCHASERS' OBLIGATIONS AT THE CLOSING.

         Each Purchaser's obligation to accept delivery of the Shares and to pay
for the Shares shall be subject to the following conditions to the extent not
waived by such Purchaser:

         8.1      REGISTRATION STATEMENT EFFECTIVE. The Registration Statement
required pursuant to Section 9 shall have become effective, and no stop order
suspending the effectiveness thereof shall have been issued and no proceedings
therefor shall be pending or threatened by the Commission.

                                       6
<PAGE>

         8.2      REPRESENTATIONS AND WARRANTIES CORRECT. The representations
and warranties made by the Company in Section 4 hereof shall be true and correct
when made, and shall be true and correct on the Closing Date.

         8.3      LEGAL OPINION. Purchasers shall have received from Heller
Ehrman White & McAuliffe, counsel to the Company, an opinion letter addressed to
the Purchasers, dated as of the Closing Date, covering the matters set forth in
Exhibit C hereto, subject to customary assumption and qualifications.

         8.4      TERMINATION. This Agreement may be terminated by any Purchaser
with respect to such Purchaser only if the Closing has not occurred by May 30,
2000.

         SECTION 9. REGISTRATION OF THE SHARES; COMPLIANCE WITH THE SECURITIES
                    ACT.

         9.1      REGISTRATION PROCEDURES AND EXPENSES. The Company is obligated
to do the following:

                  (a)      As soon as practicable following the Execution Date
and in any event no later than ten (10) days following the Execution Date, the
Company shall prepare and file with the Commission one or more registration
statements in order to register with the Commission the resale by the
Purchasers, from time to time, of the Shares through Nasdaq or the facilities of
any national securities exchange on which the Company's Common Stock is then
traded, or in privately-negotiated transactions (a "Registration Statement").
The Company shall use its best efforts to cause such Registration Statement to
be declared effective as soon thereafter as reasonably possible.

                  (b)      The Company shall prepare and file with the
Commission (i) such amendments and supplements to the Registration Statement and
the prospectus used in connection therewith, (ii) such SEC Reports and (iii)
such other filings required by the Commission, in each case as may be necessary
to keep the Registration Statement continuously effective and not misleading
until the earliest of (A) the second anniversary date of the Closing, (B) such
date as all of the Shares have been resold or (C) such time as all of the Shares
held by the Purchasers can be sold within a given three-month period pursuant to
Rule 144 under the Securities Act. Notwithstanding the foregoing, following the
effectiveness of the Registration Statement, the Company may, at any time,
suspend the effectiveness of the Registration Statement for up to no longer than
30 days, as appropriate (a "Suspension Period"), by giving notice to the
Purchasers, if the Company shall have determined that the Company may be
required to disclose any material corporate development. The Company will use
its best efforts to minimize the length of any Suspension Period.
Notwithstanding the foregoing, the Company may not suspend the effectiveness of
the Registration Statement more than twice in any twelve (12) month period. Each
Purchaser agrees that, upon receipt of any notice from the Company of a
Suspension Period, such Purchaser will not sell any Shares pursuant to the
Registration Statement until (i) such Purchaser is advised in writing by the
Company that the use of the applicable prospectus may be resumed, (ii) such
Purchaser has received copies of any additional or supplemental or amended
prospectus, if applicable, and (iii) such Purchaser has received

                                       7
<PAGE>

copies of any additional or supplemental filings which are incorporated or
deemed to be incorporated by reference in such prospectus.

                  (c)      In order to facilitate the public sale or other
disposition of all or any of the shares by each Purchaser, the Company shall
furnish to each Purchaser with respect to the Shares registered under the
Registration Statement such number of copies of prospectuses, prospectus
supplements and preliminary prospectuses as such Purchaser reasonably requests
in conformity with the requirements of the Securities Act.

                  (d)      The Company shall file any documents required of the
Company for normal blue sky clearance in states specified in writing by each
Purchaser; provided, however, that the Company shall not be required to qualify
to do business in any jurisdiction in which it is not now so qualified.

                  (e)      Other than fees and expenses, if any, of counsel or
other advisers to the Purchasers, which fees and expenses shall be borne by the
Purchasers, the Company shall bear all expenses (exclusive of any brokerage
fees, underwriting discounts and commissions) in connection with the procedures
in paragraphs (a) through (d) of this Section 9.1.

                  (f)      With a view to making available to the Purchasers the
benefits of Rule 144 promulgated under the Securities Act ("Rule 144") and any
other rule or regulation of the SEC that may at any time permit a Purchaser to
sell Shares to the public without registration or pursuant to registration, the
Company covenants and agrees to: (i) make and keep public information available,
as those terms are understood and defined in Rule 144, until the earlier of (A)
the second anniversary of the Closing Date or (B) such date as all of the Shares
shall have been resold; (ii) file with the SEC in a timely manner all reports
and other documents required of the Company under the Exchange Act; and (iii)
furnish to any Purchaser upon request, as long as the Purchaser owns any Shares,
(A) a written statement by the Company that it has complied with the reporting
requirements of the Exchange Act, (B) a copy of the most recent annual or
quarterly report of the Company, and (C) such other information as may be
reasonably requested in order to avail any Purchaser of any rule or regulation
of the SEC that permits the selling of any such Shares without registration
under the Securities Act.

         9.2      TRANSFER OF SECURITIES AFTER REGISTRATION. Each Purchaser
agrees that such Purchaser will not effect any disposition of the Shares that
would constitute a sale within the meaning of the Securities Act, except:

                  (i)      pursuant to the Registration Statement, in which case
such Purchaser shall submit the certificates evidencing the Shares to the
Company's transfer agent, accompanied by a separate "Purchaser's Certificate"
(A) in the form of Appendix III attached hereto, (B) executed by such Purchaser
or by an officer of, or other authorized person designated by, such Purchaser,
and (C) to the effect that (1) the Shares have been sold in accordance with the
Registration Statement and (2) the requirement of delivering a current
prospectus has been satisfied; or

                  (ii)     in a transaction exempt from registration under the
Securities Act, in which case such Purchaser shall, prior to effecting such
disposition, submit to the Company an

                                       8
<PAGE>

opinion of counsel in form and substance reasonably satisfactory to the Company
to the effect that the proposed transaction is in compliance with the Securities
Act.

         9.3      INDEMNIFICATION. As used in this Section 9.3 the following
terms shall have the following respective meanings:

                  (a)      "Selling Shareholder" shall mean a Purchaser of
Securities under this Agreement and any transferee of such a Purchaser who is
entitled to resell Shares pursuant to the Registration Statement;

                  (b)      "Registration Statement" shall include any final
prospectus, exhibit, supplement or amendment included in or relating to the
Registration Statement referred to in Section 9.1; and

                  (c)      "Untrue Statement" shall include any untrue statement
or alleged untrue statement, or any omission or alleged omission to state in the
Registration Statement a material fact required to be stated therein or
necessary to make the statements therein, in the light of the circumstances
under which they were made, not misleading.

         The Company agrees to indemnify and hold harmless each Selling
Shareholder from and against any losses, claims, damages or liabilities to which
such Selling Shareholder may become subject (under the Securities Act or
otherwise) insofar as such losses, claims, damages or liabilities (or actions or
proceedings in respect thereof) arise out of, or are based upon, any Untrue
Statement on or after the effective date of the Registration Statement, or on or
after the date of any prospectus or prospectus supplement or the date of any
sale by Purchaser thereunder, or arise out of any failure by the Company to
fulfill any undertaking included in the Registration Statement and the Company
will reimburse such Selling Shareholder for any reasonable legal or other
expenses reasonably incurred in investigating, defending or preparing to defend
any such action, proceeding or claim; provided, however, that the Company shall
not be liable to such Selling Shareholder in any such case to the extent that
such loss, claim, damage or liability arises out of, or is based upon, an Untrue
Statement made in such Registration Statement in reliance upon and in conformity
with written information furnished to the Company by or on behalf of such
Selling Shareholder specifically for use in preparation of the Registration
Statement, or the failure of such Selling Shareholder to comply with the
covenants and agreements contained in Section 9.1 or 9.2 hereof respecting sale
of the Shares or any statement or omission in any Prospectus that is corrected
in any subsequent prospectus that was delivered to the Selling Shareholder prior
to the pertinent sale or sales by the Selling Shareholder.

         Each Purchaser, severally and not jointly, agrees to indemnify and hold
harmless the Company (and each person, if any, who controls the Company within
the meaning of Section 15 of the Securities Act, each officer of the Company who
signs the Registration Statement and each director of the Company) from and
against any losses, claims, damages or liabilities to which the Company (or any
such officer, director or controlling person) may become subject (under the
Securities Act or otherwise), insofar as such losses, claims, damages or
liabilities (or actions or proceedings in respect thereof) arise out of, or are
based upon, any failure to comply with the covenants and agreements contained in
Section 9.1 or 9.2 hereof respecting sale of the Shares, or

                                       9
<PAGE>

any Untrue Statement contained in the Registration Statement on or after the
effective date thereof, or in any prospectus supplement as of its issue date or
date of any sale by Purchaser thereunder, if such Untrue Statement was made in
reliance upon and in conformity with written information furnished by or on
behalf of such Purchaser specifically for use in preparation of the Registration
Statement, and such Purchaser will reimburse the Company (or such officer,
director or controlling person), as the case may be, for any legal or other
expenses reasonably incurred in investigating, defending or preparing to defend
any such action, proceeding or claim; provided that in no event shall any
indemnity by a Purchaser under this Section 9.3 exceed the gross proceeds
received by such Purchaser from the sale of Shares covered by such Registration
Statement.

         Promptly after receipt by any indemnified person of a notice of a claim
or the beginning of any action in respect of which indemnity is to be sought
against an indemnifying person pursuant to this Section 9.3, such indemnified
person shall notify the indemnifying person in writing of such claim or of the
commencement of such action, and, subject to the provisions hereinafter stated,
in case any such action shall be brought against an indemnified person and such
indemnifying person shall have been notified thereof, such indemnifying person
shall be entitled to participate therein, and, to the extent it shall wish, to
assume the defense thereof, with counsel reasonably satisfactory to such
indemnified person. After notice from the indemnifying person to such
indemnified person of its election to assume the defense thereof, such
indemnifying person shall not be liable to such indemnified person for any legal
expenses subsequently incurred by such indemnified person in connection with the
defense thereof; provided, however, that if there exists or shall exist a
conflict of interest that would make it inappropriate, in the opinion of counsel
to the indemnified person, for the same counsel to represent both the
indemnified person and such indemnifying person or any affiliate or associate
thereof, the indemnified person shall be entitled to retain its own counsel at
the expense of such indemnifying person; provided, however, that no indemnifying
person shall be responsible for the fees and expenses of more than one separate
counsel for all indemnified parties.

         9.4      TERMINATION OF CONDITIONS AND OBLIGATIONS. The conditions
precedent imposed by Section 4, Section 5 or this Section 9 upon the
transferability of the Shares shall cease and terminate as to any particular
number of the Shares when such Shares shall have been sold or otherwise disposed
of in accordance with the intended method of disposition set forth in the
Registration Statement covering such Shares or at such time as an opinion of
counsel satisfactory to the Company shall have been rendered to the effect that
such conditions are not necessary in order to comply with the Securities Act.

         9.5      INFORMATION AVAILABLE. So long as the Registration Statement
is effective covering the resale of Shares owned by the Purchasers, the Company
will furnish to the Purchasers:

                  (a)      upon the request of any Purchaser, as soon as
practicable after available (but in the case of the Company's Annual Report to
Shareholders, within 150 days after the end of each fiscal year of the Company),
one copy of (i) its Annual Report to Shareholders (which Annual Report shall
contain financial statements audited in accordance with generally accepted

                                       10
<PAGE>

auditing standards certified by a national firm of certified public
accountants); (ii) its Annual Report on Form 10-K; (iii) its quarterly reports
on Form 10-Q (the foregoing, in each case, excluding exhibits); (iv) its Proxy
Statement; and (v) its current reports on Form 8-K, if any;

                  (b)      upon the request of any Purchaser, all exhibits
excluded by the parenthetical to subparagraph (a)(iii) of this Section 9.5, in
the form generally available to the public; and

                  (c)      upon the reasonable request of any Purchaser, an
adequate number of copies of the prospectuses and supplements to supply to any
other party requiring such prospectuses.

         9.6      CHANGES IN PURCHASER INFORMATION. Each Purchaser agrees to
promptly notify the Company of any changes in the information set forth in the
Registration Statement regarding Purchaser or such Purchaser's plan of
distribution set forth in such Registration Statement.

         SECTION 10. REPRESENTATIVE OF TRILOBITE LAKES CORP. ON THE COMPANY'S
                     BOARD.

         As practicable after the Closing, the Board of Directors of the Company
(the "Board") will take all steps legally necessary to elect as a member of the
Board a representative designated by Trilobite Lakes Corp. ("Trilobite"), one of
the Purchasers, who is acceptable to the other members of the Board.

         After the initial Board nominee of Trilobite has been elected, a
nominee designated by Trilobite thereafter will be nominated by the Company for
election to the Board at annual meetings of the Company's stockholders or upon
resignation, death or removal of the nominee, until the earlier of (a) such time
as Trilobite declines in writing to the Company to continue to have such
representative serving on the Board, or (b) the date on which Trilobite holds
less than half of the total number of shares which Trilobite purchases in this
Agreement. After Trilobite declines to have such representative or ceases to
hold such requisite number of shares, the nominee then serving will not be
renominated for re-election unless the Board determines on its own to renominate
such individual for election.

         SECTION 11. BROKER'S FEE.

         The Company and each Purchaser (severally and not jointly) hereby
represent that there are no brokers or finders entitled to compensation in
connection with the sale of the Shares, and shall indemnify each other for any
such fees for which they are responsible.

         SECTION 12. NOTICES.

         All notices, requests, consents and other communications hereunder
shall be in writing, shall be sent by confirmed facsimile or mailed by
first-class registered or certified airmail, or nationally recognized overnight
express courier, postage prepaid, and shall be deemed given

                                       11
<PAGE>

when so sent in the case of facsimile transmission, or when so received in the
case of mail or courier, and addressed as follows:

                  (a)     if to the Company, to:

                           Calypte Biomedical Corporation
                           1265 Harbor Bay Pkwy
                           Alameda, CA  94502
                           Attention:  President and Chief Executive Officer
                           Facsimile:  (510) 814-8505

                          with a copy so mailed to:

                           Heller Ehrman White & McAuliffe
                           525 University Avenue
                           Palo Alto, California  94301
                           Attention:  Bruce W. Jenett, Esq.
                           Facsimile:  (650) 324-0638

         or to such other person at such other place as the Company shall
designate to the Purchasers in writing; and

                  (b)      if to the Purchasers, at the address as set forth at
the end of this Agreement, or at such other address or addresses as may have
been furnished to the Company in writing.

         SECTION 13. MISCELLANEOUS.

         13.1     WAIVERS AND AMENDMENTS. Neither this Agreement nor any
provision hereof may be changed, waived, discharged, terminated, modified or
amended except upon the written consent of the Company and holders of at least a
majority of the Shares.

         13.2     HEADINGS. The headings of the various sections of this
Agreement have been inserted for convenience of reference only and shall not be
deemed to be part of this Agreement.

         13.3     SEVERABILITY. In case any provision contained in this
Agreement should be invalid, illegal or unenforceable in any respect, the
validity, legality and enforceability of the remaining provisions contained
herein shall not in any way be affected or impaired thereby.

         13.4     GOVERNING LAW. Except to the extent that the Delaware General
Corporation Law shall be applicable with respect to matters relating to the
internal corporate affairs of the Company, this Agreement shall be governed by
and construed in accordance with the laws of the State of California applicable
to contracts entered into and wholly performed within the State of California by
California residents..

                                       12
<PAGE>

         13.5     COUNTERPARTS. This Agreement may be executed in two or more
counterparts, each of which shall constitute an original, but all of which, when
taken together, shall constitute but one instrument, and shall become effective
when one or more counterparts have been signed by each party hereto and
delivered to the other parties.

         13.6     SUCCESSORS AND ASSIGNS. Except as otherwise expressly provided
herein, the provisions hereof shall inure to the benefit of, and be binding
upon, the successors, assigns, heirs, executors and administrators of the
parties hereto.

         13.7     ENTIRE AGREEMENT. This Agreement and other documents delivered
pursuant hereto, including the exhibits, constitute the full and entire
understanding and agreement between the parties with regard to the subjects
hereof and thereof.

         13.8     PAYMENT OF FEES AND EXPENSES. Each of the Company and the
Purchasers shall bear its own expenses and legal fees incurred on its behalf
with respect to this Agreement and the transactions contemplated hereby (the
"Offering"). If any action at law or in equity is necessary to enforce or
interpret the terms of this Agreement, the prevailing party shall be entitled to
reasonable attorney's fees, costs and necessary disbursements in addition to any
other relief to which such party may be entitled.

                                       13
<PAGE>

IN WITNESS WHEREOF, the parties hereto have caused this Agreement to be executed
by their duly authorized representatives as of the day and year first above
written.

                                 CALYPTE BIOMEDICAL CORPORATION

                                 By:   /s/  Nancy E. Katz
                                     ----------------------------------------
                                 Name:    Nancy E. Katz
                                 Title:   President and Chief Operating Officer

                                 PURCHASER

                                 Purchaser Name: /s/ Purchaser
                                                -----------------------------

                                 By :
                                     ----------------------------------------
                                 Name:
                                      ---------------------------------------
                                 Title:
                                       --------------------------------------
                           Address:
                                   ------------------------------------------

                                   ------------------------------------------

                                   ------------------------------------------

                           Facsimile:
                                     ----------------------------------------

                                       14<PAGE>
                                                                     Exhibit 4.2

                         CALYPTE BIOMEDICAL CORPORATION

                              BRIDGE LOAN AGREEMENT

         This Agreement is made effective as of March 2, 2000 (the "EFFECTIVE
DATE") between Calypte Biomedical Corporation, a Delaware corporation (the
"COMPANY"), and Trilobite Lakes Corp., a Delaware corporation ("LENDER").

         1.       LENDER COMMITMENT. Lender hereby commits to loan to the
Company, on an unsecured basis, under the terms and conditions hereof, up to a
total in principal amount, for all amounts so loaned, of one million dollars
($1,000,000.00), with each such loan to be evidenced by a Convertible Bridge
Promissory Note (a "BRIDGE NOTE") of the Company to Lender in the form of
EXHIBIT A attached hereto and incorporated herein by reference. The Initial
Bridge Note, as defined in Section 2(a) hereof, as well as all Additional Bridge
Notes referred to in Section 2(c) hereof, will constitute the Bridge Notes.

         2.       INITIAL DRAWDOWN AND INITIAL BRIDGE NOTE; SUBSEQUENT DRAWDOWN
REQUESTS; ADDITIONAL BRIDGE NOTES; NO REBORROWING; EQUAL RANKING OF BRIDGE
NOTES; EXTENSION OF DUE DATE OF BRIDGE NOTES; INTEREST DURING EXTENSION.

                  (a)      INITIAL DRAWDOWN AND INITIAL BRIDGE NOTE. As soon
as practicable following the execution of this agreement, Lender will loan to
the Company five hundred thousand dollars ($500,000.00) in principal amount,
as the initial drawdown by the Company from Lender pursuant to this
Agreement, receipt of which funds the Company acknowledges, in exchange for
the issuance by the Company to Lender of a Bridge Note (the "INITIAL BRIDGE
NOTE") in the form attached hereto as Exhibit A, receipt of which executed
Initial Bridge Note is acknowledged by Lender.

                  (b)      SUBSEQUENT DRAWDOWN REQUESTS. Amounts loaned to the
Company by Lender pursuant to this Agreement, beyond the initial loan by Lender
to the Company pursuant to this Agreement evidenced by the Initial Bridge Note,
will be made only in response to a written request of the Company to Lender
therefor (each such request referred to herein as a "DRAWDOWN REQUEST"). Each
Drawdown Request will (i) be given at least five (5) business days (defined as a
day when U.S. national banks are open for business) prior to the date upon which
such funds are requested, and (ii) be for a minimum of one hundred thousand
dollars ($100,000.00) or such lesser amount as is available after subtracting,
from the one million dollar ($1,000,000.00) maximum aggregate principal amount
limit set forth in Section 1 hereof, the aggregate principal amount of all
then-outstanding Bridge Notes.

                  (c)      ADDITIONAL BRIDGE NOTES. Each such additional loan
will be made under additional Convertible Promissory Notes of the Company
(the "ADDITIONAL BRIDGE NOTES") delivered by the Company, at the date of such
subsequent borrowing, to the Lender, which will be identical in form to the
Initial Bridge Note except as to the date(s) and principal amount(s) thereof,
and, as applicable, the interest rate thereof. As will be provided in the
Additional Bridge Notes, (i) the Bridge Notes will rank equally among
themselves as to all rights, (ii) all Bridge Notes will have the same due
date, which will be May 30, 2000, and (iii) the interest rate for such
Additional Bridge Notes will be 6.75%. Each such Additional Bridge Note will
be deemed subject to this Agreement upon its issuance.

<PAGE>

                  (d)      MAXIMUM TOTAL PRINCIPAL AMOUNT; NO REBORROWING. The
maximum total principal amount under all outstanding Bridge Notes, together,
will not exceed one million dollars ($1,000,000.00). No amount repaid by the
Company under any of the Bridge Notes may be reborrowed by the Company from the
Lender.

                  (e)      EQUAL RANKING OF BRIDGE NOTES. Without the express
prior written consent of Lender, (i) each of the Bridge Notes will rank equally
(PARI PASSU) among themselves as to payment, and (ii) no payment of any amount
of principal and/or interest under any Bridge Note will be paid by the Company
to Lender unless an amount prorated among the Bridge Notes in proportion to the
principal amounts of each Bridge Note is simultaneously paid by the Company to
Lender.

         3.       BRIDGE LOAN WARRANT; REGISTRATION ON FORM S-3; SEC REPORTING
AND RELATED MATTERS.

                  (a)      BRIDGE LOAN WARRANT. On the Effective Date, the
Company has issued to Lender a Warrant (the "BRIDGE LOAN WARRANT") in the form
of EXHIBIT B attached hereto and incorporated herein by reference.

                  (b)      REGISTRATION OF BRIDGE LOAN WARRANT SHARES ON FORM
S-3; TRANSFER OF BRIDGE LOAN WARRANT SHARES AFTER REGISTRATION; SEC REPORTING
AND RELATED MATTERS.

                           (i)      REGISTRATION OF BRIDGE LOAN WARRANT SHARES
ON FORM S-3. The Company will do the following:

                                    (A)      As soon as practicable following
the Effective Date, the Company will include the shares for which the Bridge
Loan Warrant is exerciseable (the "BRIDGE LOAN WARRANT Shares") in a
registration statement (the "REGISTRATION STATEMENT") which the Company will
file with the Securities and Exchange Commission (the "SEC") in connection with
a Common Stock Purchase Agreement dated as of the Effective Date (the "COMMON
STOCK PURCHASE AGREEMENT"), which agreement provides for the sale of shares of
the Company's Common Stock (the "FINANCING SHARES") to certain investors. The
Company will use its best efforts to cause such Registration Statement to be
declared effective as soon thereafter as reasonably possible.

                                    (B)      The Company will prepare and file
with the SEC (1) such amendments and supplements to the Registration Statement
and the prospectuses used in connection therewith, (2) such SEC reports and
filings required to be filed by the Company, and (3) such other filings required
by the SEC, in each case as may be necessary to keep the Registration Statement
continuously effective and not misleading until the earliest of (a) the second
anniversary date of the date of the closing of the Common Stock Purchase
Agreement, (b) such date as all of the Financing Shares have been resold or (c)
such time as all of the Financing Shares held by the holders thereof under the
Common Stock Purchase Agreement can be sold within a given three-month period
pursuant to Rule 144 under the Securities Act.

                                      -2-
<PAGE>

Notwithstanding the foregoing, following the effectiveness of the Registration
Statement, the Company may, at any time, suspend the effectiveness of the
Registration Statement for up to no longer than 30 days, as appropriate (a
"SUSPENSION PERIOD"), by giving notice to Lender, if the Company has determined
that the Company may be required to disclose any material corporate development.
The Company will use its best efforts to minimize the length of any Suspension
Period. Notwithstanding the foregoing, the Company may not suspend the
effectiveness of the Registration Statements more than twice in any twelve (12)
month period. Lender agrees that, upon receipt of any notice from the Company of
a Suspension Period, Lender will not sell any of the Bridge Loan Warrant Shares
pursuant to the Registration Statement until (1) Lender is advised in writing by
the Company that the use of the applicable prospectus may be resumed, (2) Lender
has received copies of any additional or supplemental or amended prospectus, if
applicable, and (3) Lender has received copies of any additional or supplemental
filings which are incorporated or deemed to be incorporated by reference in such
prospectus.

                                    (C)      In order to facilitate the public
sale or other disposition by Lender of all or any of the Bridge Loan Warrant
Shares, the Company will furnish to Lender, with respect to the Bridge Loan
Warrant Shares which have been registered under the Registration Statements,
such number of copies of prospectuses, prospectus supplements and preliminary
prospectuses as Lender reasonably requests in conformity with the requirements
of the Securities Act of 1933, as amended (the "SECURITIES ACT").

                                    (D)      The Company will file any documents
required of the Company for normal blue sky clearance in states specified in
writing by Lender; provided, however, that the Company will not be required to
qualify to do business in any jurisdiction in which it is not now so qualified.

                                    (E)      Other than fees and expenses, if
any, of counsel or other advisers to Lender, which fees and expenses will be
borne by Lender, the Company will bear all expenses, (exclusive of any brokerage
fees, underwriting discounts and commissions) in connection with the procedures
in this Section 3(c).

                                    (F)      With a view to making available to
Lender the benefits of Rule 144 promulgated under the Securities Act ("RULE
144") and any other rule or regulation of the SEC that may at any time permit a
Purchaser to sell the Bridge Loan Warrant Shares to the public without
registration or pursuant to registration, the Company covenants and agrees to:
(1) make and keep public information available, as those terms are understood
and defined in Rule 144, until the earlier of (a) the second anniversary of the
Closing Date or (b) such date as all of the Bridge Loan Warrant Shares have been
resold; (2) file with the SEC in a timely manner all reports and other documents
required of the Company under the Securities Exchange Act of 1934 (the "EXCHANGE
ACT"); and (3) furnish to any Purchaser upon request, as long as the Purchaser
owns any Bridge Loan Warrant Shares, (a) a written statement by the Company that
it has complied with the reporting requirements of the Exchange Act, (b) a copy
of the most recent annual or quarterly report of the Company, and (c) such other
information as may be reasonably requested in order to avail any Purchaser of
any rule or regulation of the SEC that permits the selling of any such Bridge
Loan Warrant Shares without registration under the Securities Act.

                           (ii)     TRANSFER OF BRIDGE LOAN WARRANT SHARES AFTER
REGISTRATION. Lender agrees that Lender will not effect any disposition of the
Bridge Loan

                                      -3-
<PAGE>

Warrant Shares that would constitute a sale within the meaning of the Securities
Act, except:

                                    (A)      pursuant to the applicable
Registration Statement, in which case Lender will submit the certificates
evidencing the Bridge Loan Warrant Shares to the Company's transfer agent,
accompanied by a separate certificate (1) in customary form as will be required
for such transfer of any of the Financing Shares under the Common Stock Purchase
Agreement, (2) executed by Lender or by an officer of, or other authorized
person designated by, Lender, and (3) to the effect that (a) the Bridge Loan
Warrant Shares have been sold in accordance with the applicable Registration
Statement and (b) the requirement of delivering a current prospectus has been
satisfied; or

                                    (B)      in a transaction exempt from
registration under the Securities Act, in which case Lender will, prior to
effecting such disposition, submit to the Company an opinion of counsel in form
and substance reasonably satisfactory to the Company to the effect that the
proposed transaction is in compliance with the Securities Act.

                           (iii)    SEC REPORTING AND RELATED MATTERS. The
Company will, at all times prior the declaration of effectiveness of the Form
S-3 covering the public resale of the Bridge Loan Warrant Shares:

                                    (A)      use its best efforts to make and
keep public information available, as those terms are understood and defined in
Rule 144, as promulgated under the Securities Act;

                                    (B)      use its best efforts to file with
the SEC in a timely manner all reports and other documents required of the
Company under the Securities Act and the Exchange Act;

                                    (C)      furnish to Lender, so long as
Lender owns any Bridge Loan Warrant Shares, forthwith upon request (1) a written
statement by the Company as to the Company's compliance with the reporting
requirements of Rule 144, the Securities Act and the Exchange Act (during such
time after the Company is subject to such reporting requirements), or as to its
qualification as a registrant whose securities may be resold pursuant to Form
S-3 (at any time it so qualifies), (2) a copy of the most recent annual or
quarterly report of the Company and such other reports and documents so filed by
the Company, and (3) such other information as may be reasonably requested in
availing Lender of any rule or regulation of the SEC which permits the selling
of any such securities without registration or pursuant to such form; and

                                    (D)      at all times during which the
Company is neither subject to the reporting requirements of Section 13 or 15(d)
of the Exchange Act, provide in written form, upon the written request of
Lender, or a prospective purchaser or securities of the Company from Lender, all
information required by Rule 144A(d)(4)(i) of the General Regulations
promulgated by the SEC under the Securities Act ("144A INFORMATION"); the
Company further agrees, upon written request, to cooperate with and assist
Lender or any member of the National Association of Securities Dealers, Inc.
system for Private Offerings Resales and Trading through Automated Linkages
("PORTAL") in applying to designate and thereafter maintaining the eligibility
of the Company's securities for trading through

                                      -4-
<PAGE>

PORTAL. The Company's obligations under this Section 3(c)(iii) will at all times
be contingent upon Lender's obtaining from a prospective purchaser an agreement
to take all reasonable precautions to safeguard the 144A Information from
disclosure to anyone other than employees of the prospective purchaser who
require access to the 144A Information for the sole purpose of evaluating its
purchase of the Company's securities.

         4.       USE OF PROCEEDS. All proceeds to the Company from the Bridge
Notes will be used by the Company only for operating capital, including regular
payments by the Company of debt of the Company to institutional or other
financial lenders to the Company incurred (a) prior to the Effective Date or (b)
after the Effective Date, in each case in the ordinary course of the Company's
business.

         5.       MISCELLANEOUS.

                  (a)      COUNTING OF TIME. Whenever days are to be counted
under this Agreement, the first day will not be counted and the last day will be
counted.

                  (b)      NOTICES. All notices, requests, consents and other
communications hereunder to any party will be deemed to be sufficient if
contained in a written instrument delivered in person, including delivery by
recognized express courier, fees prepaid, or sent by facsimile transmission or
duly sent by first class registered or certified mail, return receipt requested,
postage prepaid, in each case addressed as set forth below such party's
signature below, or to such other address as may hereinafter be designated in
writing by the recipient to the sender pursuant to this Section 4(b). All such
notices, requests, consents and other communications will be deemed to have been
received in the case of personal delivery, including delivery by express
courier, on the date of such delivery; in the case of facsimile transmission, on
the date of transmission; and in the case of mailing, on the third day after
deposit in the U.S. mail, proper postage prepaid.

                  (c)      TERMINATION. When the Company has repaid to Lender
all amounts owed to Lender under all Bridge Notes, whether by payment in cash,
or conversion to equity securities of the Company, or any combination thereof,
this Agreement will terminate automatically without the need for any other or
further signature of any party or any other action.

                  (d)      AMENDMENTS AND WAIVERS. Neither this Agreement or any
term hereof may be amended, modified or waived, except by written instrument
signed by the Company and by Lender. No course of dealing between the parties
will operate as a waiver of either party's rights under this Agreement. A waiver
on any one occasion will not be construed as a bar to or waiver of any right or
remedy on any future occasion. The Company acknowledges that the giving by
Lender of any notice or information to the Company, or the securing of any
consent by the Company, not required by the express terms hereof to be given or
secured, will not by implication constitute an amendment to or waiver or
modification of any provision hereof, or impose upon Lender any duty to give any
such notice or information or to secure any such consent on any future occasion.

                  (e)      ATTORNEYS' FEES. If either party hereto commences or
maintains any action at law or in equity (including counterclaims or
cross-complaints) against the other

                                      -5-
<PAGE>

party by reason of the breach or claimed breach of any term or provision of this
Agreement by such other party, then the prevailing party in such action will be
entitled to recover its reasonable attorney's fees and court costs incurred
therein from the other party to such action.

                  (f)      SUCCESSORS AND ASSIGNS. The provisions of this
Agreement will inure to the benefit of, and be binding on, each party's
respective successors and assigns. This Agreement is not assignable in whole or
in part by either party hereto without the prior written consent of both
parties, which will not be unreasonably withheld or delayed.

                  (g)      SEVERABILITY; ENTIRE AGREEMENT. The invalidity or
unenforceability of any term or provision of this Agreement will not affect the
validity or enforceability of any other term or provision hereof. The headings
in this Agreement are for convenience of reference only and will not alter or
otherwise affect the meaning of this Agreement. This Agreement and the Bridge
Notes, and the Exhibits hereto and thereto, together constitute the entire
agreement of the parties regarding the specific subject matter hereof and
supersede any and all prior understandings or agreements between the parties
with respect to such specific subject matter.

                  (h)      GOVERNING LAW. This Agreement will be governed by and
construed in accordance with the laws of the State of California, excluding that
body of law pertaining to conflict of laws or choice of law.

                           (i)      EXECUTION IN COUNTERPARTS. This Agreement
may be executed in counterparts, which together will constitute one instrument.

CALYPTE BIOMEDICAL CORPORATION                TRILOBITE LAKES CORP.

By:                                           By:
   ----------------------------------            -------------------------------
Name:                                         Name:
     --------------------------------              -----------------------------
Title:                                        Title:
      -------------------------------               ----------------------------
Date signed:  March __, 2000                  Date signed:  March __, 2000
Address:  Attention: President                Address:  Attention:
          1265 Harbor Bay Parkway                                 --------------
          Alameda, CA 94502
                                              ----------------------------------

                                              ----------------------------------
Fax:      (510) 814-8403                      Fax:        (___)-___-____

                                      -6-
<PAGE>

                                    EXHIBIT A

                               FORM OF BRIDGE NOTE

<PAGE>

                                    EXHIBIT B

                           FORM OF BRIDGE LOAN WARRANT

Source: [{"source": "alea-institute/alea-institute/kl3m-data-edgar-agreements/train-00003-of-00352.parquet"}, [{"source": "alea-institute/alea-institute/kl3m-data-edgar-agreements/train-00003-of-00352.parquet"}]]