<PAGE>

                                  EXHIBIT 4.2


THE SECURITIES REPRESENTED BY THIS CERTIFICATE AND THE SHARES OF COMMON STOCK
AND OTHER SECURITIES, IF ANY, ISSUABLE UPON EXERCISE HEREOF HAVE NOT BEEN
REGISTERED UNDER THE SECURITIES ACT OF 1933, AS AMENDED, OR ANY STATE SECURITIES
LAWS.  SUCH SECURITIES MAY NOT BE SOLD OR TRANSFERRED UNLESS REGISTERED UNDER
SUCH ACT AND ALL APPLICABLE STATE SECURITIES LAWS OR UNLESS, IN THE OPINION OF
COUNSEL SATISFACTORY TO THE COMPANY, AN EXEMPTION FROM SUCH REGISTRATIONS IS
AVAILABLE AT THE TIME OF SUCH SALE OR TRANSFER.

                                  WARRANTS TO
                             PURCHASE COMMON STOCK
                                      OF
                               AQUASEARCH, INC.

                    1997 BRIDGE WARRANT CERTIFICATE NO. __

                          VOID AFTER _________, 2000

    This certifies that, for value received, _______________ ("Buyer") or
registered assigns (the "Holder") is the owner of ______ warrants (the
"Warrants") of Aquasearch, Inc., a Colorado corporation (the "Company").  Each
Warrant shall entitle the registered holder thereof to purchase one share of the
Company's Common Stock, $0.0001 par value (the "Common Stock"), at an exercise
price (the "Exercise Price") per share of Common Stock equal to $0.50 per share
(the "Exercise Price"), at any time during the period (the "Exercise Period")
commencing on the date of this Warrant and expiring at 5:00 p.m. Honolulu,
Hawaii time, on ___________, 2000, all upon the terms and subject to the
conditions set forth herein.  After expiration of the Exercise Period, the
Holder shall have no right to purchase any Common Stock hereunder.  In the event
that the aforesaid expiration date of the Warrants falls on a day that is not a
business day, then the Warrants shall expire at 5:00 p.m. Honululu, Hawaii time
on the next succeeding business day.  For purposes hereof, the term "business
day" shall mean any day other than a Saturday, Sunday or a day on which banking
institutions in Honolulu, Hawaii are authorized or obligated by law to be
closed.

    The Warrants are being issued pursuant to a Note and Warrant Purchase
Agreement between the Company and Buyer dated as of July __, 1997 relating to
the sale by the Company and the purchase by Buyer of a Note in the aggregate
principal amount of $_________ and Warrants to purchase ______ shares of Common
Stock (the "Warrant Common Stock").  The Note and Warrant Purchase Agreement is
one of a series of Note and Warrant Purchase Agreements between the Company and
certain investors (the "Purchase Agreements") entered into in July 1997.

    The Holder, by its or his acceptance hereof, agrees with the Company that
the Warrants have been issued and all rights hereunder shall be held subject to
all of the conditions, limitations and provisions set forth herein.



<PAGE>

    1.   EXERCISE OF WARRANTS.  The rights represented by the Warrants may be
exercised in whole on one occasion at any time within the Exercise Period (a
"Warrant Exercise Date") by (i) the surrender of the Warrants (with the purchase
form at the end hereof properly executed) at the principal executive office of
the Company (or such other office or agency of the Company as it may designate
by notice in writing to the Holder at the address of the Holder appearing on the
books of the Company) along with a Notice of Exercise in the form of EXHIBIT I
hereto; and (ii) payment to the Company of the Exercise Price for the number of
shares of Common Stock specified in the above-mentioned purchase form, together
with applicable stock transfer taxes, if any.  Payment of the Exercise Price
shall be made in cash or by certified or bank check payable to the Company.  The
Warrants shall be deemed to have been exercised, in whole, immediately prior to
the close of business on the date the Warrants are surrendered and payment is
made in accordance with the foregoing provisions of this Paragraph 1, and the
person or persons in whose name or names the certificates for the Warrant Common
Stock shall be issuable upon such exercise shall become the Holder or Holders of
record of such Warrant Common Stock at that time and date.  The Warrant Common
Stock so purchased shall be delivered to the Holder within a reasonable time,
not exceeding ten business days, after the rights represented by the Warrants
shall have been so exercised.

    2.   RESTRICTIONS ON TRANSFER.  The Holder, by his or her acceptance
hereof, hereby represents and warrants to, and agrees with, the Company as
follows:  (i) the Holder has been informed that neither the Warrants, nor the
shares of Warrant Common Stock or other securities purchasable pursuant to the
Warrants, have been registered for sale under any federal or state securities
laws and that the Warrants are being offered and issued to the Holder and, upon
the exercise of the Warrants by the Holder, the Warrant Common Stock purchasable
pursuant to the Warrants will be sold to the Holder, pursuant to the exemption
from registration under the Securities Act of 1933, as amended (the "Securities
Act"); (ii) the Holder is acquiring the Warrants and will acquire the Warrant
Common Stock purchasable upon exercise of the Warrants for the Holder's own
account and not with a view to distribution thereof; (iii) neither the Warrants
nor such Warrant Common Stock may be sold, transferred, assigned, hypothecated
or otherwise disposed of, in whole or in part, unless registered under the
Securities Act and applicable state securities laws or unless, in the opinion of
counsel satisfactory to the Company, an exemption from such registrations is
available; and (iv) prior to the exercise of the Warrants the Holder shall
provide to the Company in writing such information as the Company may reasonably
request to establish that the exercise of the Warrants by the Holder is exempt
from registration under such securities laws.

    Subject to the preceding paragraph, any assignment of Warrants shall be
effected by the Holder by (i) completing and executing the Assignment Form
attached as EXHIBIT II hereto and (ii) surrendering the Warrants represented
hereby with such duly completed and executed transfer form for cancellation,
accompanied by funds sufficient to pay any transfer tax, at the office or agency
of the Company referred to in Paragraph 1; whereupon the Company shall issue, in
the name or names specified by the Holder a new Warrant or Warrants of like
tenor and representing in the aggregate rights to purchase the same number of
shares of Warrant Common Stock as are then purchasable hereunder.

    3.   PAYMENT OF TAXES.  The Company will pay any documentary stamp taxes
attributable to the initial issuance of Common Stock issuable upon the exercise
of Warrants; PROVIDED, HOWEVER, that 


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<PAGE>

the Company shall not be required to pay any tax which may be payable in 
respect of any transfer involved in the issuance or delivery of any 
certificates of shares of Warrant Common Stock in a name other than that of 
the registered Holder of Warrants in respect of which such shares are issued, 
and in such case the Company shall not be required to issue or deliver any 
certificate for shares of Warrant Common Stock or any Warrant until the 
person requesting the same has paid to the Company the amount of such tax or 
has established to the Company's satisfaction that such tax has been paid.

    4.   RESERVATION OF COMMON STOCK.  There have been reserved, and the
Company shall at all times keep reserved, out of its authorized shares of Common
Stock, a number of shares of Common Stock sufficient to provide for the exercise
of the rights of purchase represented by the Warrants, and the transfer agent
for the shares of Warrant Common Stock and every subsequent transfer agent for
any shares of Warrant Common Stock issuable upon the exercise of any of the
aforesaid rights of purchase are irrevocably authorized and directed at all
times to reserve such number of authorized shares of Common Stock as shall be
required for such purpose.  The Company agrees that all shares of Warrant Common
Stock issued upon exercise of the Warrants shall be, at the time of delivery of
the certificates for such shares against payment of the Exercise Price therefor,
validly issued and outstanding, fully paid and nonassessable.

    5.   NO RIGHTS OF SHAREHOLDER.  Prior to the exercise of any Warrants
represented hereby, the Holder, as such, shall not be entitled to any rights of
a shareholder of the Company, including, without limitation, the right to vote
or to receive dividends or other distributions, and shall not be entitled to
receive any notice of any proceedings of the Company, except as otherwise
provided herein.

    6.   ADJUSTMENTS TO EXERCISE PRICE AND NUMBER OF SHARES.  The number and
kind of securities purchasable upon the exercise of this Warrant and the
Exercise Price shall be subject to adjustment from time to time as set forth in
EXHIBIT III hereto upon the occurrence of certain events described therein.  The
provisions of  EXHIBIT III are incorporated by reference herein with the same
effect as if set forth in full herein.

    7.   NOTICES OF RECORD DATE.  In the event of any taking by the Company of
a record of its shareholders for the purpose of determining shareholders who are
entitled to receive payment of any dividend or other distribution, any right to
subscribe for, purchase or otherwise acquire any share of any class or any other
securities or property, or to receive any other right, or for the purpose of
determining shareholders who are entitled to vote in connection with any
proposed merger or consolidation of the Company with or into any other
corporation (excluding any proposed merger or consolidation in which the
shareholders of the Company immediately before such merger or consolidation will
own more than 50% of the outstanding voting stock of the surviving entity after
such merger or consolidation), or any proposed sale, lease or conveyance of all
or substantially all of the assets of the Company, or any proposed liquidation,
dissolution or winding up of the Company, then, in connection with each such
event, the Company shall mail to the Holder of this Warrant at least twenty days
prior written notice of the date on which any such record is to be taken for the
purpose of such dividend, distribution, right(s) or vote of the shareholders. 
Each such written notice shall specify the amount and character of any such
dividend, distribution or right(s), and shall set forth, in reasonable detail,
the matter requiring any such vote of the shareholders.


                                   -3-
<PAGE>

    8.   FRACTIONAL SHARES.  The Warrants may only be exercised to purchase
full shares of Warrant Common Stock and the Company shall not be required to
issue fractions of shares of Warrant Common Stock on the exercise of Warrants. 
However, if a Holder of Warrants exercises all Warrants then owned of record by
him and such exercise would result in the issuance of a fractional share, the
Company will pay to such Holder, in lieu of the issuance of any fractional share
otherwise issuable, an amount of cash based on the Market Price of the Common
Stock on the last trading day prior to the exercise date.  "Market Price" means,
on any date, the average of the last reported sale price, or, in case no such
reported takes place on such day, the average of the last reported sale prices
for the last three trading days, in either case as officially reported by the
principal securities exchange on which the Common Stock is then listed or
admitted to trading or as reported in the Nasdaq Stock Market, or, if the Common
Stock is not listed or admitted to trading on any national securities exchange
or quoted on the Nasdaq Stock Market, the closing bid quotation as furnished by
the National Association of Securities Dealers, Inc. through Nasdaq or a similar
organization if Nasdaq is no longer reporting such information, or if the Common
Stock is traded on the NASD Electronic Bulletin Board, the closing bid price as
furnished by Nasdaq, or if the the Common Stock is not quoted on Nasdaq or the
NASD Electronic Bulletin Board, as determined in good faith by resolution of the
Board of Directors of the Company, based on the best information available to it
for the day immediately preceding such issuance or sale, the day of such
issuance or sale and the day immediately after such issuance or sale.  If the
Common Stock is listed or admitted to trading on a national securities exchange
and also quoted on the Nasdaq Stock Market, the Market Price shall be determined
as hereinabove provided by reference to the prices reported in the Nasdaq Stock
Market; provided that if the Common Stock is listed or admitted to trading on
the New York Stock Exchange, the Market Price shall be determined as hereinabove
provided by reference to the prices reported by such exchange.

    9.   REGISTRATION RIGHTS.  The rights of the Holder of this Warrant and the
obligations of the Company with respect to registration under the Securities Act
and the applicable rules and regulations thereunder shall be as set forth a
Registration Rights Agreement to be entered into between the Company and the
purchasers of the Company's Exchangeable Convertible Preferred Stock (the
"Registration Rights Agreement").  The Holder of this Warrant shall be deemed to
be a party to the Registration Rights Agreement, the Warrant Common Stock shall
be deemed "Registrable Securities" (as defined in the Registration Rights
Agreement), and the Holder of this Warrant shall be deemed to be a "Holder"
under the Registration Rights Agreement (as that term is defined in the
Registration Rights Agreement), subject to all of the rights and obligations
thereunder.

    10.  MERGERS.  The Company agrees to provide the Holder of this Warrant
with at least twenty days' prior written notice of the terms and conditions of
any proposed transaction, in which the Company would (i) sell, lease, exchange,
convey or otherwise dispose of all or substantially all of its property or
business, or (ii) merge into or consolidate with any other corporation (other
than a wholly-owned subsidiary of the Company), or effect any transaction
(including a merger or other reorganization) or series of related transactions,
in which more than fifty percent (50%) of the voting power of the Company is
disposed of.  The Company will cooperate with the Holder in arranging the sale
of this Warrant in connection with any such transaction.


                                   -4-
<PAGE>

    11.  MODIFICATION AND WAIVER.  This Warrant and any provision hereof may be
changed, altered, modified, amended, supplemented, discharged or terminated only
with the written consent of the holders of a majority of the Warrants then
outstanding issued pursuant to the Purchase Agreements.  In the event that any
one or more of the provisions contained herein, or the application thereof in
any circumstance, is held invalid, illegal or unenforceable, the validity,
legality and enforceability of any such provision in every other respect and of
the remaining provisions contained herein shall not be affected or impaired
thereby, and the parties agree to cooperate with each other to insure that each
receives the economic benefits intended by any such provision that is so held to
be invalid, illegal or unenforceable.

    12.  NOTICES.  Any notice, request or other document required or permitted
to be given or delivered to the Holder hereof or the Company shall be delivered
or sent to each such Holder at its address as shown on the books of the Company
or to the Company at the address indicated therefor on the signature page of
this Warrant and shall be deemed received by the Holder upon the earlier of
actual receipt or, if sent by certified mail (postage pre-paid), five (5) days
after deposit in the U.S. mail.

    13.  BINDING EFFECT ON SUCCESSORS.  This Warrant shall be binding upon any
corporation succeeding the Company by merger, consolidation or acquisition of
all or substantially all of the Company's assets.  All of the obligations of the
Company relating to the Warrant Common Stock shall survive the exercise and
termination of this Warrant.  All of the covenants and agreements of the Company
shall inure to the benefit of the successors and assigns of the Holder hereof. 
The Company will, at the time of the exercise of this Warrant, in whole or in
part, upon request of the Holder hereof but at the Company's expense,
acknowledge in writing its continuing obligation to the Holder hereof in respect
of any rights (including, without limitation, any right to registration of the
Warrant Common Stock  in accordance with the Registration Rights Agreement) to
which the Holder hereof shall continue to be entitled after such exercise in
accordance with this Warrant; PROVIDED, HOWEVER, that the failure of the Holder
hereof to make any such request shall not affect the continuing obligation of
the Company to the Holder hereof in respect of such rights.

    14.  LOST WARRANTS OR STOCK CERTIFICATES.  The Company covenants to the
Holder hereof that upon receipt of evidence reasonably satisfactory to the
Company of the loss, theft, destruction, or mutilation of this Warrant or any
stock certificate issued upon exercise thereof and, in the case of any such
loss, theft or destruction, upon receipt of an indemnity reasonably satisfactory
to the Company, or in the case of any such mutilation upon surrender and
cancellation of such Warrant or stock certificate, the Company shall make and
deliver a new Warrant or stock certificate, or like tenor, in lieu of the lost,
stolen, destroyed or mutilated Warrant or stock certificate.

    15.  NO IMPAIRMENT.  The Company will not, by amendment of its charter or
through any reorganization, recapitalization, transfer of assets, consolidation,
merger, dissolution, issue or sale of securities or any other voluntary action,
avoid or seek to avoid the observance or performance of any of the terms to be
observed or performed hereunder by the Company, but will at all times in good
faith assist in the carrying out of all the provisions of this Warrant and in
the taking of all such action as may be necessary or appropriate in order to
protect the rights of the Holder of this Warrant against impairment.


                                   -5-
<PAGE>

    16.  DESCRIPTIVE HEADINGS.  The descriptive headings of the several
paragraphs of this Warrant are inserted for convenience only and do not
constitute a part of this Warrant.

    17.  RECOVERY OF LITIGATION COSTS.  If any legal action or other proceeding
is brought for the enforcement of this Warrant, or because of an alleged
dispute, breach, default, or misrepresentation in connection with any of the
provisions of this Warrant, the successful or prevailing party or parties shall
be entitled to recover reasonable attorneys' fees and other costs incurred in
that action or proceeding, in addition to any other relief to which it or they
may be entitled.

    18.  GOVERNING LAW.  The Warrants shall be governed by and in accordance
with the laws of the State of Hawaii without regard to the conflicts of law
principles thereof.


     IN WITNESS WHEREOF, the Company has caused this Warrant to be executed by
its duly authorized officer to take effect as of _________, 1997.


                                  AQUASEARCH, INC.


                                  By: 
                                      --------------------------------------
                                      Mark E. Huntley, Ph.D.
                                      President and Chief Executive Officer


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