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                                                                     Exhibit 4.2

                                                                       EXHIBIT A

No.                   Class D Warrants
    ------    ------


                            VOID AFTER JUNE 30, 2004

                    CLASS D WARRANT CERTIFICATE FOR PURCHASE

                                 OF COMMON STOCK

                                  PROCEPT, INC.


                  This certifies that FOR VALUE RECEIVED
-------------------------------------------------------------------------------
                             or registered assigns (the "Registered Holder") is
---------------------------- the owner of the number of Class D Warrants ("Class
D Warrants") specified above. Each Class D Warrant represented hereby initially
entitles the Registered Holder to purchase, subject to the terms and conditions
set forth in this Warrant Certificate, one fully paid and nonassessable share of
Common Stock, par value $.01 per share ("Common Stock"), of Procept, Inc., a
Delaware corporation (the "Company"), at any time between June 30, 1999, and the
Expiration Date (as hereinafter defined), upon the presentation and surrender of
this Warrant Certificate with the Subscription Form on the reverse hereof duly
executed, at the corporate offices of the Company, accompanied by payment of
$2.11 per share, as adjusted as set forth herein (the "Purchase Price") in
lawful money of the United States of America in cash or by official bank or
certified check made payable to the Company.

         In the event of certain contingencies provided for below, the Purchase
Price or the number of shares of Common Stock subject to purchase upon the
exercise of each Class D Warrant represented hereby are subject to modification
or adjustment.

                  Each Class D Warrant represented hereby is exercisable at the
option of the Registered Holder, but no fractional shares of Common Stock will
be issued. In the case of the exercise of fewer than every Class D Warrant
represented hereby, the Company shall cancel this Warrant Certificate upon the
surrender hereof and shall execute and deliver a new Warrant Certificate or
Warrant Certificates of like tenor for the balance of such Class D Warrants.

1.       DEFINITIONS.  As used herein, the following terms shall have the
following meanings, unless the context shall otherwise require:

         1.1    "Common Stock" shall mean stock of the Company of any class,
whether now or hereafter authorized, which has the right to participate in the
distribution of earnings and assets of the Company without limit as to amount or
percentage, which on the date of original issuance of this Warrant consisted of
30,000,000 authorized shares of Common Stock, par value $.01 per share.


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         1.2    The "Closing Bid Price," for each trading day, shall mean the
per share price at which the Common Stock was last exchanged on the Stock Market
(as defined below) during such trading day or, if there were no transactions on
such trading day, shall mean the average of the reported per share closing bid
and asked prices of the Common Stock on the Stock Market on such trading day.

         1.3    "Exercise Date" shall mean, as to any Class D Warrant, the date
on which the Company shall have received both (i) the Warrant Certificate
representing such Class D Warrant, with the subscription form thereon duly
executed by the Registered Holder thereof or his attorney duly authorized in
writing, and (ii) payment in cash, or by official bank or certified check made
payable to the Company, of an amount in lawful money of the United States of
America equal to the applicable Purchase Price.

         1.4    "Expiration Date" shall mean 5:00 P.M. (New York time) on June
30, 2004, or such earlier date as the Class D Warrants shall be redeemed. If
such date shall in the State of New York be a holiday or a day on which banks
are authorized to close, then the Expiration Date shall mean 5:00 P.M. (New York
time) the next following day which in the State of New York is not a holiday or
a day on which banks are authorized to close. Upon notice to all Registered
Holders of the Class D Warrants, the Company shall have the right to extend the
Expiration Date.

         1.5    "Fair Market Value" means, with respect to any security or other
asset, the fair market value set by, or determined in a manner established by,
the Board of Directors of the Company.

         1.6    "Initial Warrant Exercise Date" shall mean, as to each Class D
Warrant, June 30, 1999.

         1.7    "Market Price" shall mean the average Closing Bid Price, for
twenty (20) consecutive trading days, ending with the trading day prior to the
date as of which the Market Price is being determined, (with appropriate
adjustments for subdivisions or combinations of shares effected during such
period) provided that if the prices referred to in the definition of Closing Bid
Price cannot be determined for such period, "Market Price" shall mean Fair
Market Value (as defined above).

         1.8    "Redemption Price" shall mean the price at which the Company
may, at its option in accordance with the terms hereof, redeem the Class D
Warrants, which price shall be $0.01 per share of Common Stock subject to such
Class D Warrants.

         1.9    "Registered Holder" shall mean, as to any Class D Warrant and as
of any particular date, the person in whose name the certificate representing
the Class D Warrant shall be registered on that date on the books maintained by
the Company pursuant to Section 6.

         1.10   The "Stock Market" shall mean the principal national securities
exchange on which the Common Stock is listed or admitted to trading or, if the
Common Stock is not listed or


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admitted to trading on any national securities exchange, shall mean The Nasdaq
National Market System or The Nasdaq SmallCap Market (collectively, "Nasdaq")
or, if the Common Stock is not quoted on Nasdaq, shall mean the OTC Bulletin
Board or, if the Common Stock is not quoted on the OTC Bulletin Board, shall
mean the over-the-counter market as furnished by any NASD member firm selected
from time to time by the Company for that purpose.

         1.11   A "trading day" shall mean a day on which the Stock Market is
open for the transaction of business.

         1.12   "Transfer Agent" shall mean American Stock Transfer & Trust
Company, as the Company's transfer agent, or its authorized successor, as such.

         1.13   Unless otherwise stated, section references used within this
Warrant Certificate refer to sections of this Warrant Certificate.

2.   EXERCISE. Each Class D Warrant may be exercised by the Registered
Holder thereof at any time on or after the Initial Exercise Date, but not after
the Warrant Expiration Date, upon the terms and subject to the conditions set
forth herein. A Class D Warrant shall be deemed to have been exercised
immediately prior to the close of business on the Exercise Date and the person
entitled to receive the securities deliverable upon such exercise shall be
treated for all purposes as the holder of those securities upon the exercise of
the Class D Warrant as of the close of business on the Exercise Date. As soon as
practicable on or after the Exercise Date the Company shall deposit the proceeds
received from the exercise of a Class D Warrant. Promptly after the receipt of
such proceeds and in any event within five days thereafter, the Company, shall
cause to be issued and delivered by the Transfer Agent, to the person or persons
entitled to receive the same, a certificate or certificates for the securities
deliverable upon such exercise, (plus a certificate for any remaining
unexercised Class D Warrants of the Registered Holder).

3.       RESERVATION OF SHARES; LISTING; PAYMENT OF TAXES; ETC.

         3.1    The Company covenants that it will at all times reserve and keep
available out of its authorized Common Stock, solely for the purpose of issue
upon exercise of Class D Warrants, such number of shares of Common Stock as
shall then be issuable upon the exercise of all outstanding Class D Warrants.
The Company covenants that all shares of Common Stock which shall be issuable
upon exercise of the Class D Warrants shall, at the time of delivery (assuming
full payment of the purchase price thereof), be duly and validly issued, fully
paid, nonassessable and free from all issuance taxes, liens and charges with
respect to the issue thereof including, without limitation, adverse claims
whatsoever (with the exception of claims arising through the acts of the
Registered Holders themselves and except as arising from applicable Federal and
state securities laws), that the Company shall have paid all taxes, if any, in
respect of the original issuance thereof and that upon issuance such shares, to
the extent applicable, shall be listed on, or included in, the applicable Stock
Market.

         3.2    The Company covenants that if any securities to be reserved for
the purpose of exercise of Class D Warrants hereunder require registration with,
or the approval of, any




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governmental authority under any federal securities law before such securities
may be validly issued or delivered upon such exercise, then the Company will in
good faith and as expeditiously as reasonably possible, endeavor to secure such
registration or approval. The Company will use reasonable efforts to obtain
appropriate approvals or registrations under state "blue sky" securities laws;
provided, that the Company shall not be required to qualify as a foreign
corporation or file a general or limited consent to service of process in any
such jurisdictions or make any changes in its capital structure or any other
aspects of its business or enter into any agreements with blue sky commissions,
including any agreement to escrow shares of its capital stock. With respect to
any such securities, however, Class D Warrants may not be exercised by, or
shares of Common Stock issued to, any Registered Holder in any state in which
such exercise would be unlawful.

         3.3    The Company shall pay all documentary, stamp or similar taxes
and other similar governmental charges that may be imposed with respect to the
issuance of Class D Warrants, or the issuance or delivery of any shares upon
exercise of the Class D Warrants; provided, however, that if the shares of
Common Stock are to be delivered in a name other than the name of the Registered
Holder of the Warrant Certificate representing any Class D Warrant being
exercised, then no such delivery shall be made unless the person requesting the
same has paid to the Company the amount of transfer taxes or charges incident
thereto, if any or provided satisfactory evidence that no amount is due.

         3.4    The Company is hereby irrevocably authorized to requisition the
Company's Transfer Agent from time to time for certificates representing shares
of Common Stock issuable upon exercise of the Class D Warrants, and the Company
will authorize the Transfer Agent to comply with all such proper requisitions.

4.       EXCHANGE AND REGISTRATION OF TRANSFER.

         4.1    Warrant Certificates may be exchanged for other Warrant
Certificates representing an equal aggregate number of Class D Warrants of the
same class (provided the Company shall not exchange Warrant Certificates for new
Warrant Certificates in denominations of fewer than fifty thousand (50,000)
underlying shares) or may be transferred in whole or in part. Warrant
Certificates to be exchanged shall be surrendered to the Company at its
Corporate Office, and upon satisfaction of the terms and provisions hereof, the
Company shall execute, issue and deliver in exchange therefor, the Warrant
Certificate or Certificates that the Registered Holder making the exchange shall
be entitled to receive.

         4.2    The Company shall keep at its office books in which, subject to
such reasonable regulations as it may prescribe, it shall register Warrant
Certificates and any transfers thereof in accordance with its regular practice.
Upon due presentment for registration of transfer of any Warrant Certificate at
such office, the Company shall execute and deliver to the transferee or
transferees a new Warrant Certificate or Certificates representing an equal
aggregate number of Class D Warrants.


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         4.3    With respect to all Warrant Certificates presented for
registration or transfer, or for exchange or exercise, the subscription form on
the reverse thereof shall be duly endorsed, or be accompanied by a written
instrument or instruments of transfer and subscription, in form satisfactory to
the Company, duly executed by the Registered Holder or his attorney-in-fact duly
authorized in writing.

         4.4    Prior to due presentment for registration of transfer thereof,
the Company may deem and treat the Registered Holder of any Warrant Certificate
as the absolute owner thereof and of each Class D Warrant represented thereby
(notwithstanding any notations of ownership or writing thereon made by anyone
other than a duly authorized officer of the Company) for all purposes and shall
not be affected by any notice to the contrary.

5.       LOSS OR MUTILATION. Upon receipt by the Company of evidence
satisfactory to it of the ownership of and loss, theft, destruction or
mutilation of any Warrant Certificate and (in case of loss, theft or
destruction) of indemnity reasonably satisfactory to it and (in the case of
mutilation) upon surrender and cancellation thereof, the Company shall execute
and (in the absence of notice to the Company that the Warrant Certificate has
been acquired by a bona fide purchaser) and deliver to the Registered Holder in
lieu thereof a new Warrant Certificate of like tenor representing an equal
aggregate number of Class D Warrants. Applicants for a substitute Warrant
Certificate shall comply with such other reasonable regulations and pay such
other reasonable charges as the Company may prescribe.

6.       REDEMPTION.

         6.1    At any time after June 30, 2000, on no fewer than sixty (60)
days' prior written notice to Registered Holders of the Class D Warrants being
redeemed, the Company may, at its option, redeem the Class D Warrants at the
Redemption Price, provided the Market Price of the Common Stock as of the third
business day prior to the date of notice of redemption (which shall be the date
of mailing of such notice) exceeds 250% of the Purchase Price per share of
Common Stock subject to a Class D Warrant. All outstanding Class D Warrants must
be redeemed if any are redeemed. The date fixed for redemption of the Class D
Warrants is referred to herein as the "Redemption Date."

         6.2    If the conditions set forth in Subsection 6.1 are met, and the
Company desires to exercise its right to redeem the Class D Warrants, it shall
request the Company to mail a notice of redemption to each of the Registered
Holders of the Class D Warrants to be redeemed, first class, postage prepaid,
not later than the sixtieth day before the date fixed for redemption, at their
last address as shall appear on the records maintained pursuant to Subsection
4.2. Any notice mailed in the manner provided herein shall be conclusively
presumed to have been duly given whether or not the Registered Holder receives
such notice.

         6.3    The notice of redemption shall specify (i) the redemption price,
(ii) the Redemption Date, (iii) the place where the Warrant Certificates shall
be delivered and the redemption price paid, (iv) that the right to exercise the
Class D Warrant shall terminate at 5:00 P.M. (New York time) on the business day
immediately preceding the Redemption Date. No


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failure to mail such notice nor any defect therein or in the mailing thereof
shall affect the validity of the proceedings for such redemption except as to a
Registered Holder (A) to whom notice was not mailed or (B) whose notice was
defective. An affidavit of the Secretary or an Assistant Secretary of the
Company that notice of redemption has been mailed shall, in the absence of
fraud, be prima facie evidence of the facts stated therein.

         6.4    Any right to exercise a Class D Warrant shall terminate at 5:00
P.M. (New York time) on the business day immediately preceding the Redemption
Date. On and after the Redemption Date, Holders of the Class D Warrants shall
have no further rights except to receive, upon surrender of the Class D Warrant,
the Redemption Price.

         6.5    From and after the Redemption Date, the Company shall, at the
place specified in the notice of redemption, upon presentation and surrender to
the Company by or on behalf of the Registered Holder thereof of one or more
Warrant Certificates evidencing Class D Warrants to be redeemed, deliver or
cause to be delivered to or upon the written order of such Registered Holder a
sum in cash equal to the redemption price of such Class D Warrants. From and
after the Redemption Date and upon the deposit or setting aside by the Company
of a sum sufficient to redeem all the Class D Warrants called for redemption,
such Class D Warrants shall expire and become void and all rights hereunder and
under the Warrant Certificates, except the right to receive payment of the
redemption price, shall cease.

7.       ADJUSTMENT OF PURCHASE PRICE AND NUMBER OF SHARES OF COMMON STOCK OR
CLASS D WARRANTS. Upon each adjustment of the Purchase Price pursuant to this
Section 7, the total number of shares of Common Stock purchasable upon the
exercise of each Class D Warrant shall (subject to the provisions contained in
Subsection 7.3) be such number of shares (calculated to the nearest tenth)
purchasable at the Purchase Price in effect immediately prior to such adjustment
multiplied by a fraction, the numerator of which shall be the Purchase Price in
effect immediately prior to such adjustment and the denominator of which shall
be the Purchase Price in effect immediately after such adjustment.

         7.1    Except as otherwise provided herein, in the event the Company
shall, at any time or from time to time after the date hereof, (i) sell or issue
any shares of Common Stock for a consideration per share less than either (a)
the Purchase Price in effect on the date of such sale or issuance or (b) the
Market Price of the Common Stock as of the date of the sale or issuance, (ii)
issue any shares of Common Stock as a stock dividend to the holders of Common
Stock, or (iii) subdivide or combine the outstanding shares of Common Stock into
a greater or fewer number of shares (any such sale, issuance, subdivision or
combination being herein called a "Change of Shares"), then, and thereafter upon
each further Change of Shares, the Purchase Price in effect immediately prior to
such Change of Shares shall be changed to a price (rounded to the nearest cent)
determined by multiplying the Purchase Price in effect immediately prior thereto
by the quotient of (x) the sum of (A) the number of shares of Common Stock
outstanding immediately prior to the sale or issuance of such additional shares
or such subdivision or combination plus (B) the number of shares of Common Stock
that the aggregate consideration received (determined as provided in
Paragraph 7.7(vi)) for the issuance of such additional shares would purchase at
the


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greater of (1) the Purchase Price in effect on the date of such issuance or
(2) the Market Price as of such date, divided by (y) the number of shares of
Common Stock outstanding immediately after the sale or issuance of such
additional shares or such subdivision or combination. Such adjustment shall
be made successively whenever any such issuance is made.

         7.2    In case of any reclassification, capital reorganization or
other change of outstanding shares of Common Stock, or in case of any
consolidation or merger of the Company with or into another entity (other
than a consolidation or merger in which the Company is the continuing entity
and which does not result in any reclassification, capital reorganization or
other change of outstanding shares of Common Stock other than the number
thereof), or in case of any sale or conveyance to another entity of the
property of the Company as, or substantially as, an entirety (other than a
sale/leaseback, mortgage or other financing transaction), the Company shall
cause effective provision to be made so that each holder of a Class D Warrant
then outstanding shall have the right thereafter, by exercising such Class D
Warrant, upon the terms and conditions specified in the Class D Warrants and
in lieu of the shares of Common Stock immediately theretofore purchasable
upon exercise of the Class D Warrants, to purchase the kind and number of
shares of stock or other securities or property (including cash) receivable
upon such reclassification, capital reorganization or other change,
consolidation, merger, sale or conveyance by a holder of the number of shares
of Common Stock that might have been purchased upon exercise of such Class D
Warrant immediately prior to such reclassification, capital reorganization or
other change, consolidation, merger, sale or conveyance. Any such provision
shall include provision for adjustments that shall be as nearly equivalent as
may be practicable to the adjustments provided for in this Section 7. The
Company shall not effect any such consolidation, merger or sale unless prior
to, or simultaneously with, the consummation thereof the successor (if other
than the Company) resulting from such consolidation or merger or the entity
purchasing assets or other appropriate entity shall assume, by written
instrument executed and delivered to the Company, the obligation to deliver
to the holder of each Class D Warrant such shares of stock, securities or
assets as, in accordance with the foregoing provisions, such holders may be
entitled to purchase and the other obligations under this Agreement. The
foregoing provisions shall similarly apply to successive reclassifications,
capital reorganizations and other changes of outstanding shares of Common
Stock and to successive consolidations, mergers, sales or conveyances.

         7.3    If, at any time or from time to time, the Company shall issue or
distribute to the holders of shares of Common Stock evidence of its
indebtedness, any other securities of the Company or any cash, property or other
assets (excluding an issuance or distribution governed by one of the preceding
Subsections of this Section 7 and also excluding cash dividends or cash
distributions paid out of net profits legally available therefor in the full
amount thereof (any such non-excluded event being herein called a "Special
Dividend")), then in each case the Registered Holders of the Class D Warrants
shall be entitled to a proportionate share of any such Special Dividend as
though they were the holders of the number of shares of Common Stock of the
Company for which their Class D Warrants are exercisable as of the record date
fixed for the determination of the holders of Common Stock of the Company
entitled to receive such Special Dividend.


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         7.4    The Company may elect, upon any adjustment of the Purchase Price
hereunder, to adjust the number of Class D Warrants outstanding, in lieu of the
adjustment in the number of shares of Common Stock purchasable upon the exercise
of each Class D Warrant as hereinabove provided, so that each Class D Warrant
outstanding after such adjustment shall represent the right to purchase one
share of Common Stock. Each Class D Warrant held of record prior to such
adjustment of the number of Class D Warrants shall become that number of Class D
Warrants (calculated to the nearest tenth) determined by multiplying the number
one by a fraction, the numerator of which shall be the Purchase Price in effect
immediately prior to such adjustment and the denominator of which shall be the
Purchase Price in effect immediately after such adjustment. Upon each adjustment
of the number of Class D Warrants pursuant to this Section 7, the Company shall,
as promptly as practicable, cause to be distributed to each Registered Holder of
Warrant Certificates on the date of such adjustment Warrant Certificates
evidencing, subject to Section 8, the number of additional Class D Warrants to
which such Holder shall be entitled as a result of such adjustment or, at the
option of the Company, cause to be distributed to such Holder in substitution
and replacement for the Warrant Certificates held by him prior to the date of
adjustment (and upon surrender thereof, if required by the Company) new Warrant
Certificates evidencing the number of Class D Warrants to which such Holder
shall be entitled after such adjustment.

         7.5    Irrespective of any adjustments or changes in the Purchase Price
or the number of shares of Common Stock purchasable upon exercise of the Class D
Warrants, the Warrant Certificates theretofore and thereafter issued shall,
unless the Company shall exercise its option to issue new Warrant Certificates
pursuant to Subsection 7.4, continue to express the same Purchase Price per
share, number of shares purchasable thereunder and Redemption Price therefor as
when the same were originally issued.

         7.6    After each adjustment of the Purchase Price pursuant to this
Section 7, the Company will promptly prepare a certificate signed by the
Chairman or President, and by the Treasurer or an Assistant Treasurer or the
Secretary or an Assistant Secretary, of the Company setting forth: (i) the
Purchase Price as so adjusted, (ii) the number of shares of Common Stock
purchasable upon exercise of each Class D Warrant after such adjustment, and, if
the Company shall have elected to adjust the number of Class D Warrants pursuant
to Subsection 7.4, the number of Class D Warrants to which the registered holder
of each Class D Warrant shall then be entitled, and the adjustment in Redemption
Price resulting therefrom, and (iii) a brief statement of the facts accounting
for such adjustment. The Company will promptly send such certificate by ordinary
first class mail to each Registered Holder of Class D Warrants at his or her
last address as it shall appear on the registry books of the Company. No failure
to mail such notice nor any defect therein or in the mailing thereof shall
affect the validity of such adjustment. The affidavit of an officer of the
Company or the Secretary or an Assistant Secretary of the Company that such
notice has been mailed shall, in the absence of fraud, be prima facie evidence
of the facts stated therein. The Company may rely on the information in the
certificate as true and correct and has no duty or obligation to independently
verify the amounts or calculations set forth therein.


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         7.7    For purposes of Subsection 7.1, the following provisions (i) to
(vi) shall also be applicable:

                (i)   the number of shares of Common Stock deemed outstanding
at any given time shall include all shares of capital stock convertible into,
or exchangeable for, Common Stock (on an as converted basis) as well as all
shares of Common Stock issuable upon the exercise of (x) any convertible
debt, (y) warrants outstanding on the date hereof and (z) options outstanding
on the date hereof.

                (ii)  No adjustment of the Purchase Price shall be made unless
such adjustment would require an increase or decrease of at least $.01 in such
price; provided that any adjustments which by reason of this Paragraph (ii) are
not required to be made shall be carried forward and shall be made at the time
of and together with the next subsequent adjustment which, together with
adjustments so carried forward, shall require an increase or decrease of at
least $.01 in the Purchase Price then in effect hereunder.

                (iii) In case of (A) the sale by the Company (including as a
component of a unit) of any rights or warrants to subscribe for or purchase, or
any options for the purchase of, Common Stock or any securities convertible into
or exchangeable for Common Stock (such securities convertible, exercisable or
exchangeable into Common Stock being herein called "Convertible Securities"), or
(B) the issuance by the Company, without the receipt by the Company of any
consideration therefor, of any rights or warrants to subscribe for or purchase,
or any options for the purchase of, Common Stock or Convertible Securities,
whether or not such rights, warrants or options, or the right to convert or
exchange such Convertible Securities, are immediately exercisable, and the
consideration per share for which Common Stock is issuable upon the exercise of
such rights, warrants or options or upon the conversion or exchange of such
Convertible Securities (determined by dividing (x) the minimum aggregate
consideration, as set forth in the instrument relating thereto without regard to
any antidilution or similar provisions contained therein for a subsequent
adjustment of such amount, payable to the Company upon the exercise of such
rights, warrants or options, plus the consideration received by the Company for
the issuance or sale of such rights, warrants or options, plus, in the case of
such Convertible Securities, the minimum aggregate amount, as set forth in the
instrument relating thereto without regard to any antidilution or similar
provisions contained therein for a subsequent adjustment of such amount, of
additional consideration, if any, other than such Convertible Securities,
payable upon the conversion or exchange thereof, by (y) the total maximum
number, as set forth in the instrument relating thereto without regard to any
antidilution or similar provisions contained therein for a subsequent adjustment
of such amount, of shares of Common Stock issuable upon the exercise of such
rights, warrants or options or upon the conversion or exchange of such
Convertible Securities issuable upon the exercise of such rights, warrants or
options) is less than either the Purchase Price or the Market Price of the
Common Stock as of the date of the issuance or sale of such rights, warrants or
options, then such total maximum number of shares of Common Stock issuable upon
the exercise of such rights, warrants or options or upon the conversion or
exchange of such Convertible Securities (as of the date of the issuance or sale
of such rights, warrants or options) shall be deemed to be "Common Stock" for
purposes of


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Subsection 7.1 and shall be deemed to have been sold for an amount equal to such
consideration per share and shall cause an adjustment to be made in accordance
with Subsection 7.1.

                (iv)  In case of the sale or other issuance by the Company of
any Convertible Securities, whether or not the right of conversion or exchange
thereunder is immediately exercisable, and the price per share for which Common
Stock is issuable upon the conversion or exchange of such Convertible Securities
(determined by dividing (A) the total amount of consideration received by the
Company for the sale of such Convertible Securities, plus the minimum aggregate
amount, as set forth in the instrument relating thereto without regard to any
antidilution or similar provisions contained therein for a subsequent adjustment
of such amount, of additional consideration, if any, other than such Convertible
Securities, payable upon the conversion or exchange thereof, by (B) the total
maximum number, as set forth in the instrument relating thereto without regard
to any antidilution or similar provisions contained therein for a subsequent
adjustment of such amount, of shares of Common Stock issuable upon the
conversion or exchange of such Convertible Securities) is less than either the
Purchase Price or the Market Price of the Common Stock as of the date of the
sale of such Convertible Securities, then such total maximum number of shares of
Common Stock issuable upon the conversion or exchange of such Convertible
Securities (as of the date of the sale of such Convertible Securities) shall be
deemed to be "Common Stock" for purposes of Subsection 7.1 and shall be deemed
to have been sold for an amount equal to such consideration per share and shall
cause an adjustment to be made in accordance with Subsection 7.1.

                (v)   In case the Company shall modify the rights of conversion,
exchange or exercise of any of the securities referred to in Paragraphs (iii) or
(iv) of this Subsection 7.7 or any other securities of the Company convertible,
exchangeable or exercisable for shares of Common Stock, for any reason other
than an event that would require adjustment to prevent dilution, so that the
consideration per share received by the Company after such modification is less
than either the Purchase Price or the Market Price as of the date prior to such
modification, then such securities, to the extent not theretofore exercised,
converted or exchanged, shall be deemed to have expired or terminated
immediately prior to the date of such modification and the Company shall be
deemed, for purposes of calculating any adjustments pursuant to this Section 7,
to have issued such new securities upon such new terms on the date of
modification. Such adjustment shall become effective as of the date upon which
such modification shall take effect. On the expiration or cancellation of any
such right, warrant or option or the termination or cancellation of any such
right to convert or exchange any such Convertible Securities, the Purchase Price
then in effect hereunder shall forthwith be readjusted to such Purchase Price as
would have obtained (A) had the adjustments made upon the issuance or sale of
such rights, warrants, options or Convertible Securities been made upon the
basis of the issuance of only the number of shares of Common Stock theretofore
actually delivered (and the total consideration received therefor) upon the
exercise of such rights, warrants or options or upon the conversion or exchange
of such Convertible Securities and (B) had adjustments been made on the basis of
the Purchase Price as adjusted under clause (A) of this sentence for all
transactions (which would have affected such adjusted Purchase Price) made after
the issuance or sale of such rights, warrants, options or Convertible
Securities.


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                (vi)   In case of the sale of any shares of Common Stock, any
Convertible Securities, any rights or warrants to subscribe for or purchase, or
any options for the purchase of, Common Stock or Convertible Securities, the
consideration received by the Company therefor shall be deemed to be the gross
sales price therefor without deducting therefrom any expense paid or incurred by
the Company or any underwriting discounts or commissions or concessions paid or
allowed by the Company in connection therewith. In the event that any securities
shall be issued in connection with any other securities of the Company, together
comprising one integral transaction in which no specific consideration is
allocated among the securities, then each of such securities shall be deemed to
have been issued for such consideration as the Board of Directors of the Company
determines in good faith; provided, however that if holders of more than of ten
percent (10%) of the then outstanding Class D Warrants disagree with such
determination, the Company shall retain an independent investment banking firm
for the purpose of obtaining an appraisal.

         7.8    Notwithstanding any other provision hereof, no adjustment to the
Purchase Price of the Class D Warrants or to the number of shares of Common
Stock purchasable upon the exercise of each Class D Warrant will be made:

                (i)   upon the exercise of any of the options outstanding on the
date hereof under the Company's existing stock option plans; or

                (ii)  upon the issuance or exercise of options which may
hereafter be granted with the approval of the Board of Directors, or exercised,
under any employee benefit plan of the Corporation to officers, directors,
consultants or employees, but only with respect to such options as are
exercisable at prices no lower than the Market Price of the Common Stock as of
the date of grant thereof; or

                (iii) upon issuance or exercise of the Placement Warrants, or
the Advisory Warrants, (as defined in the Placement Agency Agreement between the
Corporation and Paramount Capital, Inc. dated as of October 26, 1997), pursuant
to currently existing rights under Subscription Agreements or other documents to
receive additional shares of Common Stock as a dividend or pursuant to
anti-dilution provisions or upon the exercise of any other of the currently
outstanding warrants of the Company; or

                (iv)  upon the issuance or sale of Common Stock or Convertible
Securities pursuant to the exercise of any rights, options or warrants to
receive, subscribe for or purchase, or any options for the purchase of, Common
Stock or Convertible Securities, whether or not such rights, warrants or options
were outstanding on the date of the original sale of the Class D Warrants or
were thereafter issued or sold, provided that an adjustment was either made or
not required to be made in accordance with Subsections 7.1 and 7.3 in connection
with the issuance or sale of such securities or any modification of the terms
thereof; or

                (v)   upon the issuance or sale of Common Stock upon conversion
or exchange of any Convertible Securities, provided that any adjustments
required to be made upon the issuance or sale of such Convertible Securities or
any modification of the terms thereof were


                                       11
<PAGE>


so made, and whether or not such Convertible Securities were outstanding on the
date of the original sale of the Class D Warrants or were thereafter issued or
sold; or

                (vi)  upon the issuance of stock which may hereafter be
purchased or sold with the approval of the Board of Directors, under the 1993
Employee Stock Purchase Plan of the Company to officers, directors, consultants
or employees, but only with respect to such shares as are purchased and/or sold
in accordance with the current plan and at prices no lower than eighty-five
percent (85%) of the Closing Bid Price (or, if the prices referenced in the
definition of Closing Bid Price cannot be determined, 85% of the Fair Market
Value) of the Common Stock as of the date of purchase and/or sale thereof.

Paragraph 7.7(v) shall nevertheless apply to any modification of the rights of
conversion, exchange or exercise of any of the securities referred to in
Paragraphs (i), (ii) and (iii) of this Subsection 7.8, except for modifications
required by the original terms of such securities.

         7.9    As used in this Section 7, the term "Common Stock" shall mean
and include the Company's Common Stock authorized on the date of the original
issue hereof and shall also include any capital stock of any class of the
Company thereafter authorized which shall not be limited to a fixed sum or
percentage in respect of the rights of the holders thereof to participate in
dividends and in the distribution of assets upon the voluntary liquidation,
dissolution or winding up of the Company; provided, however, that the shares
issuable upon exercise of the Class D Warrants shall include only shares of such
class designated in the Company's Certificate of Incorporation, as amended, as
Common Stock on the date of the original issue hereof or (i), in the case of any
reclassification, change, consolidation, merger, sale or conveyance of the
character referred to in Subsection 7.2, the stock, securities or property
provided for in such section or (ii), in the case of any reclassification or
change in the outstanding shares of Common Stock issuable upon exercise of the
Class D Warrants as a result of a subdivision or combination or consisting of a
change in par value, or from par value to no par value, or from no par value to
par value, such shares of Common Stock as so reclassified or changed.

         7.10     Any determination as to whether an adjustment in the Purchase
Price in effect hereunder is required pursuant to Section 7, or as to the amount
of any such adjustment, if required, shall be binding upon the holders of the
Class D Warrants and the Company if made in good faith by the Board of Directors
of the Company, except as otherwise contemplated hereby.

         7.11   If and whenever the Company shall grant to the holders of Common
Stock, as such, rights or warrants to subscribe for or to purchase, or any
options for the purchase of, Common Stock or securities convertible into or
exchangeable for or carrying a right, warrant or option to purchase Common
Stock, the Company may at its option elect concurrently therewith to grant to
each Registered Holder as of the record date for such transaction of the Class D
Warrants then outstanding, the rights, warrants or options to which each
Registered Holder would have been entitled if, on the record date used to
determine the stockholders entitled to the rights, warrants or options being
granted by the Company, the Registered Holder were the holder of record of the
number of whole shares of Common Stock then issuable upon exercise of his or


                                       12
<PAGE>


her Class D Warrants. If the Company shall so elect under this Subsection 7.11,
then such grant by the Company to the holders of the Class D Warrants shall be
in lieu of any adjustment which otherwise might be called for pursuant to this
Section 7.

8.       FRACTIONAL WARRANTS AND FRACTIONAL SHARES. If the number of shares of
Common Stock purchasable upon the exercise of each Class D Warrant is adjusted
pursuant to Section 7, the Company nevertheless shall not be required to issue
fractions of shares, upon exercise of the Class D Warrants or otherwise, nor to
distribute certificates that evidence fractional shares. With respect to any
fraction of a share called for upon any exercise hereof, the Company shall pay
to the Registered Holder an amount in cash equal to such fraction multiplied by
the Fair Market Value of one (1) share of Common Stock as of the date of
exercise.

9.       WARRANT HOLDERS NOT DEEMED STOCKHOLDERS. No holder of Class D Warrants
shall, as such, be entitled to vote or to receive dividends or be deemed the
holder of Common Stock that may at any time be issuable upon exercise of such
Class D Warrants for any purpose whatsoever, nor shall anything contained herein
be construed to confer upon the holder of Class D Warrants, as such, any of the
rights of a stockholder of the Company or any right to vote for the election of
directors or upon any matter submitted to stockholders at any meeting thereof,
or to give or withhold consent to any corporate action (whether upon any
recapitalization, issue or reclassification of stock, change of par value or
change of stock to no par value, consolidation, merger or conveyance or
otherwise), or to receive notice of meetings, or to receive dividends or
subscription rights, until such Holder shall have exercised such Class D
Warrants and been issued shares of Common Stock in accordance with the
provisions hereof.

10.      REGISTRATION RIGHTS. The Registered Holder of this Class D Warrant
shall have the registration rights as provided in Section 5 of the Subscription
Agreement (the "Subscription Agreement") dated as of the date hereof between the
Company and such Registered Holder. The Class D Warrants represented hereby
shall not be exercisable by a Registered Holder in any state where such exercise
would be unlawful.

11.      AGREEMENT OF WARRANT HOLDERS. Every holder of any Class D Warrant, by
his acceptance thereof, consents and agrees with the Company and every other
holder of any Class D Warrant that:

         (a)    The Class D Warrants are transferable only on the registry
books of the Company by the Registered Holder thereof in person or by his or her
attorney duly authorized in writing and only if the Warrant Certificates
representing such Class D Warrants are surrendered at the office of the Company,
duly endorsed or accompanied by a proper instrument of transfer satisfactory to
the Company, in its sole discretion, together with payment of any applicable
transfer taxes; and

         (b)    The Company may deem and treat the person in whose name the
Warrant Certificate is registered as the holder and as the absolute, true and
lawful owner of the Class D Warrants represented thereby for all purposes, and
the Company shall not be affected by any notice or knowledge to the contrary,
except as otherwise expressly provided in Section 4.


                                       13
<PAGE>


12.      CANCELLATION OF WARRANT CERTIFICATES. If the Company shall purchase or
acquire any Class D Warrant or Class D Warrants, the Warrant Certificate or
Warrant Certificates evidencing the same, by redemption or otherwise, shall
thereupon be delivered to the Company and canceled by it and retired. The
Company shall also cancel the Warrant Certificate or Warrant Certificates
following exercise of any or all of the Class D Warrants represented thereby or
delivered to it for transfer, split up, combination or exchange.

13.      NOTICES. All notices, requests, consents and other communications
hereunder shall be in writing and shall be deemed to have been made when
delivered or mailed by means of first class registered or certified mail,
postage prepaid as follows: if to the Registered Holder of a Warrant
Certificate, at the address of such holder as shown on the registry books
maintained by the Company; and if to the Company, at 840 Memorial Drive,
Cambridge, Massachusetts, 02139, or at such other address as may have been
furnished to the Registered Holders in writing by the Company.

14.      GOVERNING LAW. This Agreement shall be governed by, and construed in
accordance with, the laws of the State of New York, without reference to
principles of conflict of laws.

15.      BINDING EFFECT. This Agreement shall be binding upon and inure to the
benefit of the Company and its respective successors and assigns, and the
holders from time to time of the Warrants represented by this Warrant
Certificate. Nothing in this Agreement is intended nor shall be construed to
confer upon any other person any right, remedy or claim, in equity or at law, or
to impose upon any other person any duty, liability or obligation.


                                       14
<PAGE>


                  IN WITNESS WHEREOF, the Company has caused this Warrant
Certificate to be duly executed, manually or in facsimile, by a duly authorized
officer.

                                  PROCEPT, INC.


Dated:                            By:
      --------------------------     ----------------------------------------




                                       15
<PAGE>


                    [FORM OF REVERSE OF WARRANT CERTIFICATE]


SUBSCRIPTION FORM

To Be Executed by the Registered Holder
in Order to Exercise Class D Warrants


                  The undersigned Registered Holder hereby irrevocably elects to
exercise           Class D Warrants represented by this Warrant Certificate, and
         --------
to purchase the securities issuable upon the exercise of such Class D Warrants,
and requests that certificates for such securities shall be issued in the name
of

PLEASE INSERT SOCIAL SECURITY OR OTHER IDENTIFYING NUMBER

------------------------------------------
------------------------------------------
------------------------------------------
------------------------------------------
[please print or type name and address]

and be delivered to

------------------------------------------
------------------------------------------
------------------------------------------
------------------------------------------
[please print or type name and address]


and if such number of Class D Warrants shall not be all the Class D Warrants
evidenced by this Warrant Certificate, that a new Warrant Certificate for the
balance of such Class D Warrants be registered in the name of, and delivered to,
the Registered Holder at the address stated below.


                                       16
<PAGE>


                                   ASSIGNMENT


To Be Executed by the Registered Holder
in Order to Assign Class D Warrants


FOR VALUE RECEIVED,                                               hereby sells,
                    ---------------------------------------------
assigns and transfers unto


PLEASE INSERT SOCIAL SECURITY OR OTHER IDENTIFYING NUMBER


------------------------------------------
------------------------------------------
------------------------------------------
------------------------------------------
[please print or type name and address]

                                 of the Class D Warrants represented by this
--------------------------------
Warrant Certificate, and hereby irrevocably constitutes and appoints
------------------------------------

-------------------------------------------------------------------------------
Attorney to transfer this Warrant Certificate on the books of the Company, with
full power of substitution in the premises.


Dated:                             X
        -------------------------

        -----------------------------------
                                     Signature Guaranteed


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


THE SIGNATURE TO THE ASSIGNMENT OR THE SUBSCRIPTION FORM MUST CORRESPOND TO THE
NAME AS WRITTEN UPON THE FACE OF THIS WARRANT CERTIFICATE IN EVERY PARTICULAR,
WITHOUT ALTERATION OR ENLARGEMENT OR ANY CHANGE WHATSOEVER, AND MUST BE
GUARANTEED BY A MEMBER OF THE MEDALLION STAMP PROGRAM.


                                       17
<PAGE>


                                                                     EXHIBIT 4.2


                     Schedule of Holders of Class D Warrants

         The following individuals and entities are holders of Class D Warrants
with respect to an aggregate of 924,525 shares of Common Stock:

 1. Ross D. Ain

 2. Palmetto Partners, Ltd.

 3. Richard A. Lydecker

 4. Arthur Nagle

 5. Osterweis Revocable Trust

 6. Prager, Dreifuss & Partners

 7. The Keys Foundation

 8. David W. Ruttenberg

 9. J.F. Shea & Co., Inc.

10. Donald E. & Virginia V. Vinson

11. Bruno Widmer

12. Aries Domestic Fund, L.P.

13. The Aries Trust

                                            1