Document:

REGISTRATION RIGHTS AGREEMENT
                          -----------------------------

         This Registration Rights Agreement (this "Agreement") is made and
entered into as of March 29, 2000, among SafeScience, Inc., a Nevada corporation
(the "Company"), and the investors signatory hereto (each such investor is a
"Purchaser" and all such investors are, collectively, the "Purchasers").

         This Agreement is made pursuant to the Securities Purchase Agreement,
dated as of the date hereof among the Company and the Purchasers (the "Purchase
Agreement").

                  The Company and the Purchasers hereby agree as follows:

Definitions

         Capitalized terms used and not otherwise defined herein that are
defined in the Purchase Agreement shall have the meanings given such terms in
the Purchase Agreement. As used in this Agreement, the following terms shall
have the following meanings:

         "Adjustable Warrants" shall have the meaning set forth in the Purchase
Agreement.

         "Affiliate" means, with respect to any Person, any other Person that
directly or indirectly controls or is controlled by or under common control with
such Person. For the purposes of this definition, "control," when used with
respect to any Person, means the possession, direct or indirect, of the power to
direct or cause the direction of the management and policies of such Person,
whether through the ownership of voting securities, by contract or otherwise;
and the terms of "affiliated," "controlling" and "controlled" have meanings
correlative to the foregoing.

         "Business Day" " shall have the meaning set forth in the Purchase
Agreement.

         "Closing Date" shall have the meaning set forth in the Purchase
Agreement.

         "Closing Warrants" shall have the meaning set forth in the Purchase
Agreement.

         "Commission" means the Securities and Exchange Commission.

         "Common Stock" means the Company's common stock, $.01 par value, or
such securities that such stock shall hereafter be reclassified into.

         "Effectiveness Date" means the 90th day following the Closing Date.

         "Effectiveness Period" shall have the meaning set forth in Section
2(a).

         "Exchange Act" means the Securities Exchange Act of 1934, as amended.

         "Filing Date" means the 30th day following the Closing Date.

         "Holder" or "Holders" means the holder or holders, as the case may be,
from time to time of Registrable Securities.

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         "Indemnified Party" shall have the meaning set forth in Section 5(c).

         "Indemnifying Party" shall have the meaning set forth in Section 5(c).

         "Losses" shall have the meaning set forth in Section 5(a).

         "Person" means an individual or a corporation, partnership, trust,
incorporated or unincorporated association, joint venture, limited liability
company, joint stock company, government (or an agency or political subdivision
thereof) or other entity of any kind.

         "Proceeding" means an action, claim, suit, investigation or proceeding
(including, without limitation, an investigation or partial proceeding, such as
a deposition), whether commenced or threatened.

         "Prospectus" means the prospectus included in the Registration
Statement (including, without limitation, a prospectus that includes any
information previously omitted from a prospectus filed as part of an effective
registration statement in reliance upon Rule 430A promulgated under the
Securities Act), as amended or supplemented by any prospectus supplement, with
respect to the terms of the offering of any portion of the Registrable
Securities covered by the Registration Statement, and all other amendments and
supplements to the Prospectus, including post-effective amendments, and all
material incorporated by reference or deemed to be incorporated by reference in
such Prospectus.

         "Registrable Securities" means (i) the Shares, (ii) the shares of
Common Stock issuable upon exercise in full of the Warrants and (iii) any shares
of capital stock issued or issuable with respect to the Shares or the shares of
Common Stock issuable upon exercise of the Warrants as a result of any stock
split, stock dividend, recapitalization, exchange or similar event or otherwise,
without regard to any limitations on exercises of the Warrants.

         "Registration Statement" means the registration statement and any
additional registration statements contemplated by Section 2(a), including (in
each case) the Prospectus, amendments and supplements to such registration
statement or Prospectus, including pre- and post-effective amendments, all
exhibits thereto, and all material incorporated by reference or deemed to be
incorporated by reference in such registration statement.

         "Rule 144" means Rule 144 promulgated by the Commission pursuant to the
Securities Act, as such Rule may be amended from time to time, or any similar
rule or regulation hereafter adopted by the Commission having substantially the
same effect as such Rule.

         "Rule 415" means Rule 415 promulgated by the Commission pursuant to the
Securities Act, as such Rule may be amended from time to time, or any similar
rule or regulation hereafter adopted by the Commission having substantially the
same effect as such Rule.

         "Rule 424" means Rule 424 promulgated by the Commission pursuant to the
Securities Act, as such Rule may be amended from time to time, or any similar
rule or regulation hereafter adopted by the Commission having substantially the
same effect as such Rule.

<PAGE>

         "Securities Act" means the Securities Act of 1933, as amended, and the
rules and regulations promulgated thereunder.

         "Shares" means the shares of Common Stock issued to the Purchasers on
the Closing Date pursuant to the Purchase Agreement.

         "Special Counsel" means one special counsel to all of the Holders, for
which the Holders will be reimbursed by the Company pursuant to Section 4.

         "Vesting Date" shall have the meaning set forth in the Adjustable
Warrants.

         "Warrants" means the Closing Warrants and the Adjustable Warrants.

Shelf Registration

(a) On or prior to the Filing Date, the Company shall prepare and file with the
Commission a "Shelf" Registration Statement covering the resale of all
Registrable Securities for an offering to be made on a continuous basis pursuant
to Rule 415. The Registration Statement shall be on Form S-3 (except if the
Company is not then eligible to register for resale the Registrable Securities
on Form S-3, in which case such registration shall be on another appropriate
form in accordance herewith as set forth in this section) and shall contain
(except if otherwise directed by the Holders) the "Plan of Distribution"
attached hereto as Annex A. The Company shall use its best efforts to cause the
Registration Statement to be declared effective under the Securities Act as
promptly as possible after the filing thereof, but in any event prior to the
Effectiveness Date, and shall use its best efforts to keep such Registration
Statement continuously effective under the Securities Act until the date which
is two years after the date that such Registration Statement is declared
effective by the Commission or such earlier date when all Registrable Securities
covered by such Registration Statement have been sold or may be sold without
volume restrictions pursuant to Rule 144(k) (the "Effectiveness Period"),
provided, that the Company shall not be deemed to have used its best efforts to
keep the Registration Statement effective during the Effectiveness Period if it
voluntarily takes any action that would result in the Holders not being able to
sell the Registrable Securities covered by such Registration Statement during
the Effectiveness Period, unless such action is required under applicable law or
the Company has filed a post-effective amendment to the Registration Statement
and the Commission has not declared it effective. In the event that Form S-3 is
not available for the registration of the resale of Registrable Securities
hereunder, the Company shall (i) register the resale of the Registrable
Securities on another appropriate form and (ii) register the resale of the
Registrable Securities on Form S-3 as soon as such form is available(which shall
not be later than May 23, 2000), provided, that the Company shall maintain the
effectiveness of the Registration Statement then in effect until such time as a
Registration Statement on Form S-3 covering the Registrable Securities has been
declared effective by the Commission.

(b) In order to account for the fact that the number of shares of Common Stock
that are issuable upon exercise of the Adjustable Warrants is determined in part
upon the market price of the Common Stock on a Vesting Date, the initial
Registration Statement to be filed hereunder shall include (but not be limited
to) a number of shares of Common Stock equal to no less than the sum of (i) the
number of shares issuable upon exercise of the Adjustable

<PAGE>

Warrants on the First Vesting Date (as defined in the Adjustable Warrants)
assuming, for the purposes of this subsection that, on the First Vesting Date:
(A) the Adjustment Price (as defined in the Adjustable Warrants) is 50% of the
Per Share Market Value for the Trading Day immediately preceding the Closing
Date or the Trading Day immediately preceding the Filing Date, whichever is
greater, and (B) the Applicable Share Number (as defined in the Adjustable
Warrants) equals the entire number of Shares purchased under the Purchase
Agreement, (ii) the number of shares issuable upon exercise in full of the
Closing Warrants and (iii) the Shares.

(c) In the event the number of shares available under a Registration Statement
filed pursuant to Section 2(a) is insufficient to cover all of the Registrable
Securities which such Registration Statement is required to cover, the Company
shall file a new Registration Statement (on the short form available therefor,
if applicable), so as to cover at least that number of shares of Common Stock
equal to the sum of (x) 200% of the number of shares issuable upon exercise of
the Adjustable Warrants (without regard to any limitations on exercise) as of
the date immediately preceding the date such amendment or new Registration
Statement is filed with the Commission, plus (y) the number of shares of Common
Stock issuable upon exercise of the Closing Warrants (without regard to any
limitations on exercise) as of the date immediately preceding the date such or
new Registration Statement is filed with the Commission, plus (z) the number of
Registrable Securities held by the Purchasers as of the date immediately
preceding the date on which such or new Registration Statement is filed with the
Commission (assuming such Registrable Securities are not already registered
under an effective Registration Statement previously filed by the Company with
the Commission), in each case, as soon as practicable, but in any event not
later than fifteen (15) business days after the necessity therefor arises. The
Company shall cause such new Registration Statement to become effective as soon
as practicable following the filing thereof but, in any event, no later than the
60th day after the necessity therefor arises. For purposes of the foregoing
provision, the number of shares available under a Registration Statement shall
be deemed insufficient to cover all of the Registrable Securities if the number
of Registrable Securities issued or issuable upon exercise of the Warrants
covered by such Registration Statement is greater than the sum of (a) the
quotient determined by dividing (i) the number of shares of Common Stock
available for resale under the Registration Statement to cover shares issued or
issuable upon exercise of the Adjustable Warrants by (ii) 1.5 and (b) the number
of shares of Common Stock available for resale under the Registration Statement
to cover shares issued or issuable upon exercise of the Closing Warrants. For
purposes of the calculation set forth in the foregoing sentence, any
restrictions on the exercise of the Warrants shall be disregarded and such
calculation shall assume that the Warrants are then exercisable for, shares of
Common Stock at the then prevailing Exercise Price (as defined in the applicable
Warrants).

(d) If (a) the initial Registration Statement is not filed on or prior to the
Filing Date (if the Company files such Registration Statement without affording
the Holder the opportunity to review and comment on the same as required by
Section 3(a) hereof, the Company shall not be deemed to have satisfied this
clause (a)), or (b) the Company fails to file with the Commission a request for
acceleration in accordance with Rule 461 promulgated under the Securities Act,
within five days of the date that the Company is notified (orally or in writing,
whichever is earlier) by the Commission that a Registration Statement will not
be "reviewed," or not subject to further review, or (c) the initial Registration
Statement filed hereunder is not declared effective by the Commission on or
prior to the Effectiveness Date, or (d) after a

<PAGE>

Registration Statement is filed with and declared effective by the Commission,
such Registration Statement ceases to be effective as to all Registrable
Securities required to be registered per clause (b) of this Section 2(d) at any
time prior to the expiration of the Effectiveness Period without being succeeded
within fifteen days by an amendment to such Registration Statement or by a
subsequent Registration Statement filed within 60 days with and declared
effective by the Commission, or (e) the Common Stock shall be delisted or
suspended from trading on the Nasdaq SmallCap Market ("NASDAQ") or on the New
York Stock Exchange, American Stock Exchange or the Nasdaq National Market
(each, a "Subsequent Market") for more than three days (which need not be
consecutive days), or (f) the exercise rights of the Holders pursuant to the
Warrants are suspended for any reason, or (g) an amendment to a Registration
Statement is not filed by the Company with the Commission within ten days of the
Commission's notifying the Company that such amendment is required in order for
such Registration Statement to be declared effective (any such failure or breach
being referred to as an "Event," and for purposes of clauses (a), (c), (f) the
date on which such Event occurs, or for purposes of clause (b) the date on which
such five day period is exceeded, or for purposes of clauses (d) and (g) the
date which such 15 or 10 day-period is exceeded, respectively, or for purposes
of clause (e) the date on which such three day-period is exceeded, being
referred to as "Event Date"), then, in any such case, as partial relief for the
damages suffered therefrom by the Holder (which remedy shall not be exclusive of
any other remedies available at law or in equity), the Company shall on the
Event Date and on each monthly anniversary thereof until the triggering Event is
cured, pay to the Holder an amount in cash, as liquidated damages for the
estimated cost to the Holders of not having liquid securities in the time
contemplated by the Transaction Documents and not as a penalty, equal to 1.5% of
the purchase price paid by such Holder for its Shares pursuant to the Purchase
Agreement. If the applicable Event has not been cured by the 180th day following
the Event Date, on the 180th day following the Event Date and each monthly
anniversary thereof until the applicable Event is cured, the Company shall pay
to each Holder 5.0% of the purchase price paid by such Holder for its Shares
pursuant to the Purchase Agreement, in cash, as liquidated damages and not as a
penalty. The payments to which the Holders shall be entitled pursuant to this
Section are referred to herein as "Registration Delay Payments." Registration
Delay Payments shall be calculated on a cumulative basis and paid within five
(5) Business Days of (i) the Event Date and (ii) each monthly anniversary
thereof. The liquidated damages shall apply on a pro-rata basis for any portion
of a month prior to the cure of an Event. If the Company fails to make
Registration Delay Payments in a timely manner, such Registration Delay Payments
shall bear interest at the rate of 2.0% per month (or the maximum rate permitted
by law), pro-rated for partial months, until paid in full.

Registration Procedures
-----------------------

         In connection with the Company's registration obligations hereunder,
the Company shall:

(e)  Not less than five Business Days prior to the filing of the Registration
Statement or any related Prospectus or less than two Business Days prior to the
filing of any amendment or supplement thereto (including any document that would
be incorporated or deemed to be incorporated therein by reference), the Company
shall, (i) furnish to the Holders and their Special Counsel copies of all such
documents proposed to be filed, which documents (other than those incorporated
or deemed to be incorporated by reference) will be subject to the review of such
Holders and their Special Counsel, and (ii) cause its officers and directors,

<PAGE>

counsel and independent certified public accountants to respond to such
inquiries as shall be necessary, in the reasonable opinion of respective counsel
to such to conduct a reasonable investigation within the meaning of the
Securities Act. The Company shall not file the Registration Statement or any
such Prospectus or any amendments or supplements thereto to which the Holders of
a majority of the Registrable Securities and their Special Counsel shall
reasonably object. The Holders and their Special Counsel shall have 5 Business
Days in the case of the Registration Statement or any related Prospectus or 2
Business Days in the case of any amendment or supplement thereto to which they
may reasonably object.

(f) (i) Prepare and file with the Commission such amendments, including
post-effective amendments, to the Registration Statement and the Prospectus used
in connection therewith as may be necessary to keep the Registration Statement
continuously effective as to the applicable Registrable Securities for the
Effectiveness Period and prepare and file with the Commission such additional
Registration Statements in order to register for resale under the Securities Act
all of the Registrable Securities; (ii) cause the related Prospectus to be
amended or supplemented by any required Prospectus supplement, and as so
supplemented or amended to be filed pursuant to Rule 424; (iii) respond as
promptly as reasonably possible, and in any event within ten Business Days, to
any comments received from the Commission with respect to the Registration
Statement or any amendment thereto and as promptly as reasonably possible
provide the Holders true and complete copies of all correspondence from and to
the Commission relating to the Registration Statement; and (iv) comply in all
material respects with the provisions of the Securities Act and the Exchange Act
with respect to the disposition of all Registrable Securities covered by the
Registration Statement during the applicable period in accordance with the
intended methods of disposition by the Holders thereof set forth in the
Registration Statement as so amended or in such Prospectus as so supplemented.

(g) [Intentionally left blank]

(h) Notify the Holders of Registrable Securities to be sold and their Special
Counsel as promptly as reasonably possible (and, in the case of (i)(A) below,
not less than five Business Days prior to such filing) and (if requested by any
such Person) confirm such notice in writing no later than one Business Day
following the day (i)(A) when a Prospectus or any Prospectus supplement or
post-effective amendment to the Registration Statement is proposed to be filed;
(B) when the Commission notifies the Company whether there will be a "review" of
such Registration Statement and whenever the Commission comments in writing on
such Registration Statement (the Company shall provide true and complete copies
thereof and all written responses thereto to each of the Holders); and (C) with
respect to the Registration Statement or any post-effective amendment, when the
same has become effective; (ii) of any request by the Commission or any other
Federal or state governmental authority for amendments or supplements to the
Registration Statement or Prospectus or for additional information; (iii) of the
issuance by the Commission of any stop order suspending the effectiveness of the
Registration Statement covering any or all of the Registrable Securities or the
initiation of any Proceedings for that purpose; (iv) if at any time any of the
representations and warranties of the Company contained in any agreement
contemplated hereby ceases to be true and correct in all material respects; (v)
of the receipt by the Company of any notification with respect to the suspension
of the qualification or exemption from qualification of any of the Registrable
Securities for sale in any jurisdiction, or the initiation or threatening of any
Proceeding for such

<PAGE>

purpose; and (vi) of the occurrence of any event or passage of time that makes
the financial statements included in the Registration Statement ineligible for
inclusion therein or any statement made in the Registration Statement or
Prospectus or any document incorporated or deemed to be incorporated therein by
reference untrue in any material respect or that requires any revisions to the
Registration Statement, Prospectus or other documents so that, in the case of
the Registration Statement or the Prospectus, as the case may be, it will not
contain any untrue statement of a material fact or omit to state any material
fact required to be stated therein or necessary to make the statements therein,
in light of the circumstances under which they were made, not misleading.

(i) Use its best efforts to avoid the issuance of, or, if issued, obtain the
withdrawal of (i) any order suspending the effectiveness of the Registration
Statement, or (ii) any suspension of the qualification (or exemption from
qualification) of any of the Registrable Securities for sale in any
jurisdiction, at the earliest practicable moment.

(j) Furnish to each Holder and their Special Counsel, without charge, at least
one conformed copy of each Registration Statement and each amendment thereto,
including financial statements and schedules, all documents incorporated or
deemed to be incorporated therein by reference, and all exhibits to the extent
requested by such Person (including those previously furnished or incorporated
by reference) promptly after the filing of such documents with the Commission.

(k) Promptly deliver to each Holder and their Special Counsel, without charge,
as many copies of the Prospectus or Prospectuses (including each form of
prospectus) and each amendment or supplement thereto as such Persons may
reasonably request. Upon effectiveness of the Registration Statement, the
Company hereby consents to the use of such Prospectus and each amendment or
supplement thereto by each of the selling Holders in connection with the
offering and sale of the Registrable Securities covered by such Prospectus and
any amendment or supplement thereto.

(l) Prior to any public offering of Registrable Securities, use its best efforts
to register or qualify or cooperate with the selling Holders and their Special
Counsel in connection with the registration or qualification (or exemption from
such registration or qualification) of such Registrable Securities for offer and
sale under the securities or Blue Sky laws of such jurisdictions within the
United States as any Holder requests in writing, to keep each such registration
or qualification (or exemption therefrom) effective during the Effectiveness
Period and to do any and all other acts or things necessary or advisable to
enable the disposition in such jurisdictions of the Registrable Securities
covered by a Registration Statement; provided, that the Company shall not be
required to qualify generally to do business in any jurisdiction where it is not
then so qualified or subject the Company to any material tax in any such
jurisdiction where it is not then so subject.

(m) Cooperate with the Holders to facilitate the timely preparation and delivery
of certificates representing Registrable Securities to be delivered to a
transferee pursuant to a Registration Statement, which certificates shall be
free, to the extent permitted by the Purchase Agreement, of all restrictive
legends, and to enable such Registrable Securities to be in such denominations
and registered in such names as any such Holders may request.

<PAGE>

(n) Upon the occurrence of any event contemplated by Section 3(d)(vi), as
promptly as reasonably possible, prepare a supplement or amendment, including a
post-effective amendment, to the Registration Statement or a supplement to the
related Prospectus or any document incorporated or deemed to be incorporated
therein by reference, and file any other required document so that, as
thereafter delivered, neither the Registration Statement nor such Prospectus
will contain an untrue statement of a material fact or omit to state a material
fact required to be stated therein or necessary to make the statements therein,
in light of the circumstances under which they were made, not misleading.

(o) Comply with all applicable rules and regulations of the Commission.

(p) The Company may require each selling Holder to furnish to the Company a
certified statement as to the number of shares of Common Stock beneficially
owned by such Holder and, if requested by the Commission, the controlling person
thereof.

Registration Expenses. All fees and expenses incident to the performance of or
compliance with this Agreement by the Company shall be borne by the Company
whether or not any Registrable Securities are sold pursuant to the Registration
Statement. The fees and expenses referred to in the foregoing sentence shall
include, without limitation, (i) all registration and filing fees (including,
without limitation, fees and expenses (A) with respect to filings required to be
made with the NASDAQ and any Subsequent Market on which the Common Stock is then
listed for trading, and (B) in compliance with state securities or Blue Sky laws
(including, without limitation, fees and disbursements of counsel for the
Holders in connection with Blue Sky qualifications or exemptions of the
Registrable Securities and determination of the eligibility of the Registrable
Securities for investment under the laws of such jurisdictions as the Holders of
a majority of Registrable Securities may designate)), (ii) printing expenses
(including, without limitation, expenses of printing certificates for
Registrable Securities and of printing prospectuses if the printing of
prospectuses is requested by the holders of a majority of the Registrable
Securities included in the Registration Statement), (iii) messenger, telephone
and delivery expenses, (iv) fees and disbursements of counsel for the Company
and Special Counsel for the Holders (in the case of the latter, up to a maximum
of $7,500), (v) Securities Act liability insurance, if the Company so desires
such insurance, and (vi) fees and expenses of all other Persons retained by the
Company in connection with the consummation of the transactions contemplated by
this Agreement. In addition, the Company shall be responsible for all of its
internal expenses incurred in connection with the consummation of the
transactions contemplated by this Agreement (including, without limitation, all
salaries and expenses of its officers and employees performing legal or
accounting duties), the expense of any annual audit and the fees and expenses
incurred in connection with the listing of the Registrable Securities on any
securities exchange as required hereunder.

Indemnification

(q)  Indemnification by the Company. The Company shall, notwithstanding any
termination of this Agreement, indemnify and hold harmless each Holder, the
officers, directors, agents, brokers (including brokers who offer and sell
Registrable Securities as principal as a result of a pledge or any failure to
perform under a margin call of Common Stock), investment advisors and employees
of each of them, each Person who controls any such Holder

<PAGE>

(within the meaning of Section 15 of the Securities Act or Section 20 of the
Exchange Act) and the officers, directors, agents and employees of each such
controlling Person, to the fullest extent permitted by applicable law, from and
against any and all losses, claims, damages, liabilities, costs (including,
without limitation, costs of preparation and attorneys' fees) and expenses
(collectively, "Losses"), as incurred, arising out of or relating to any untrue
or alleged untrue statement of a material fact contained in the Registration
Statement, any Prospectus or any form of prospectus or in any amendment or
supplement thereto or in any preliminary prospectus, or arising out of or
relating to any omission or alleged omission of a material fact required to be
stated therein or necessary to make the statements therein (in the case of any
Prospectus or form of prospectus or supplement thereto, in light of the
circumstances under which they were made) not misleading, except to the extent,
but only to the extent, that (1) such untrue statements or omissions are based
solely upon information regarding such Holder furnished in writing to the
Company by such Holder expressly for use therein, or to the extent that such
information relates to such Holder or such Holder's proposed method of
distribution of Registrable Securities and was reviewed and expressly approved
in writing by such Holder expressly for use in the Registration Statement, such
Prospectus or such form of Prospectus or in any amendment or supplement thereto
or (2) in the case of an occurrence of an event of the type specified in Section
3(d)(ii)-(vi), the use by such Holder of an outdated or defective Prospectus
after the Company has notified such Holder in writing that the Prospectus is
outdated or defective and prior to the receipt by such Holder of the Advice
contemplated in Section 6(e). The Company shall notify the Holders promptly of
the institution, threat or assertion of any Proceeding of which the Company is
aware in connection with the transactions contemplated by this Agreement.

(r) Indemnification by Holders. Each Holder shall, severally and not jointly,
indemnify and hold harmless the Company, its directors, officers, agents and
employees, each Person who controls the Company (within the meaning of Section
15 of the Securities Act and Section 20 of the Exchange Act), and the directors,
officers, agents or employees of such controlling Persons, to the fullest extent
permitted by applicable law, from and against all Losses (as determined by a
court of competent jurisdiction in a final judgment not subject to appeal or
review) arising solely out of or based solely upon any untrue statement of a
material fact contained in the Registration Statement, any Prospectus, or any
form of prospectus, or in any amendment or supplement thereto, or arising solely
out of or based solely upon any omission of a material fact required to be
stated therein or necessary to make the statements therein not misleading to the
extent, but only to the extent, that such untrue statement or omission is
contained in any information so furnished in writing by such Holder to the
Company specifically for inclusion in the Registration Statement or such
Prospectus or to the extent that such information relates to such Holder or such
Holder's proposed method of distribution of Registrable Securities and was
reviewed and expressly approved in writing by such Holder expressly for use in
the Registration Statement, such Prospectus or such form of Prospectus, or in
any amendment or supplement thereto. In no event shall the liability of any
selling Holder hereunder be greater in amount than the dollar amount of the net
proceeds received by such Holder upon the sale of the Registrable Securities
giving rise to such indemnification obligation.

(s) Conduct of Indemnification Proceedings. If any Proceeding shall be brought
or asserted against any Person entitled to indemnity hereunder (an "Indemnified
Party"), such Indemnified Party shall promptly notify the Person from whom
indemnity is sought (the "Indemnifying Party") in writing, and the Indemnifying
Party shall assume the defense thereof,

<PAGE>

including the employment of counsel reasonably satisfactory to the Indemnified
Party and the payment of all fees and expenses incurred in connection with
defense thereof; provided, that the failure of any Indemnified Party to give
such notice shall not relieve the Indemnifying Party of its obligations or
liabilities pursuant to this Agreement, except (and only) to the extent that it
shall be finally determined by a court of competent jurisdiction (which
determination is not subject to appeal or further review) that such failure
shall have proximately and materially adversely prejudiced the Indemnifying
Party.

An Indemnified Party shall have the right to employ separate counsel in any such
Proceeding and to participate in the defense thereof, but the fees and expenses
of such counsel shall be at the expense of such Indemnified Party or Parties
unless: (1) the Indemnifying Party has agreed in writing to pay such fees and
expenses; or (2) the Indemnifying Party shall have failed promptly to assume the
defense of such Proceeding and to employ counsel reasonably satisfactory to such
Indemnified Party in any such Proceeding; or (3) the named parties to any such
Proceeding (including any impleaded parties) include both such Indemnified Party
and the Indemnifying Party, and such Indemnified Party shall have been advised
by counsel that a conflict of interest is likely to exist if the same counsel
were to represent such Indemnified Party and the Indemnifying Party (in which
case, if such Indemnified Party notifies the Indemnifying Party in writing that
it elects to employ separate counsel at the expense of the Indemnifying Party,
the Indemnifying Party shall not have the right to assume the defense thereof
and such counsel shall be at the expense of the Indemnifying Party). The
Indemnifying Party shall not be liable for any settlement of any such Proceeding
effected without its written consent, which consent shall not be unreasonably
withheld. No Indemnifying Party shall, without the prior written consent of the
Indemnified Party, effect any settlement of any pending Proceeding in respect of
which any Indemnified Party is a party, unless such settlement includes an
unconditional release of such Indemnified Party from all liability on claims
that are the subject matter of such Proceeding.

         All fees and expenses of the Indemnified Party (including reasonable
fees and expenses to the extent incurred in connection with investigating or
preparing to defend such Proceeding in a manner not inconsistent with this
Section) shall be paid to the Indemnified Party, as incurred, within ten
Business Days of written notice thereof to the Indemnifying Party (regardless of
whether it is ultimately determined that an Indemnified Party is not entitled to
indemnification hereunder; provided, that the Indemnifying Party may require
such Indemnified Party to undertake to reimburse all such fees and expenses to
the extent it is finally judicially determined that such Indemnified Party is
not entitled to indemnification hereunder).

(t)  Contribution. If a claim for indemnification under Section 5(a) or 5(b) is
unavailable to an Indemnified Party (by reason of public policy or otherwise),
then each Indemnifying Party, in lieu of indemnifying such Indemnified Party,
shall contribute to the amount paid or payable by such Indemnified Party as a
result of such Losses, in such proportion as is appropriate to reflect the
relative fault of the Indemnifying Party and Indemnified Party in connection
with the actions, statements or omissions that resulted in such Losses as well
as any other relevant equitable considerations and relative benefits received.
The relative fault of such Indemnifying Party and Indemnified Party shall be
determined by reference to, among other things, whether any action in question,
including any untrue or alleged untrue statement of a material fact or omission
or alleged omission of a material fact, has been taken or made by, or

<PAGE>

relates to information supplied by, such Indemnifying Party or Indemnified
Party, and the parties' relative intent, knowledge, access to information and
opportunity to correct or prevent such action, statement or omission. The amount
paid or payable by a party as a result of any Losses shall be deemed to include,
subject to the limitations set forth in Section 5(c), any reasonable attorneys'
or other reasonable fees or expenses incurred by such party in connection with
any Proceeding to the extent such party would have been indemnified for such
fees or expenses if the indemnification provided for in this Section was
available to such party in accordance with its terms.

         The parties hereto agree that it would not be just and equitable if
contribution pursuant to this Section 5(d) were determined by pro rata
allocation or by any other method of allocation that does not take into account
the equitable considerations referred to in the immediately preceding paragraph.
Notwithstanding the provisions of this Section 5(d), no Holder shall be required
to contribute, in the aggregate, any amount in excess of the amount by which the
proceeds actually received by such Holder from the sale of the Registrable
Securities subject to the Proceeding exceeds the amount of any damages that such
Holder has otherwise been required to pay by reason of such untrue or alleged
untrue statement or omission or alleged omission. No Person guilty of fraudulent
misrepresentation (within the meaning of Section 11(f) of the Securities Act)
shall be entitled to contribution from any Person who was not guilty of such
fraudulent misrepresentation.

         The indemnity and contribution agreements contained in this Section are
in addition to any liability that the Indemnifying Parties may have to the
Indemnified Parties.

Miscellaneous

(u)  Remedies. In the event of a breach by the Company or by a Holder, of any of
their obligations under this Agreement, each Holder or the Company, as the case
may be, in addition to being entitled to exercise all rights granted by law and
under this Agreement, including recovery of damages, will be entitled to
specific performance of its rights under this Agreement. The Company and each
Holder agree that monetary damages would not provide adequate compensation for
any losses incurred by reason of a breach by it of any of the provisions of this
Agreement and hereby further agrees that, in the event of any action for
specific performance in respect of such breach, it shall waive the defense that
a remedy at law would be adequate.

(v)  No Inconsistent Agreements. Neither the Company nor any of its subsidiaries
has entered, as of the date hereof, nor shall the Company or any of its
subsidiaries, on or after the date of this Agreement, enter into any agreement
with respect to its securities that is inconsistent with the rights granted to
the Holders in this Agreement or otherwise conflicts with the provisions hereof.
Except as and to the extent specified in Schedule 6(b) hereto, neither the
Company nor any of its subsidiaries has previously entered into any agreement
granting any registration rights with respect to any of its securities to any
Person.

(w) No Piggyback on Registrations. Except as and to the extent specified in
Schedule 6(b) hereto, neither the Company nor any of its security holders (other
than the Holders in such capacity pursuant hereto) may include securities of the
Company in the Registration

<PAGE>

Statement other than the Registrable Securities, and the Company shall not after
the date hereof enter into any agreement providing any such right to any of its
security holders.

(x) Compliance. Each Holder covenants and agrees that it will comply with the
prospectus delivery requirements of the Securities Act as applicable to it in
connection with sales of Registrable Securities pursuant to the Registration
Statement.

(y) Discontinued Disposition. Each Holder agrees by its acquisition of such
Registrable Securities that, upon receipt of a notice from the Company of the
occurrence of any event of the kind described in Sections 3(d)(ii), 3(d)(iii),
3(d)(iv), 3(d)(v) or 3(d)(vi), such Holder will forthwith discontinue
disposition of such Registrable Securities under the Registration Statement
until such Holder's receipt of the copies of the supplemented Prospectus and/or
amended Registration Statement contemplated by Section 3(j), or until it is
advised in writing (the "Advice") by the Company that the use of the applicable
Prospectus may be resumed, and, in either case, has received copies of any
additional or supplemental filings that are incorporated or deemed to be
incorporated by reference in such Prospectus or Registration Statement. The
Company may provide appropriate stop orders to enforce the provisions of this
paragraph.

(z) Piggy-Back Registrations. If at any time during the Effectiveness Period
there is not an effective Registration Statement covering all of the Registrable
Securities and the Company shall determine to prepare and file with the
Commission a registration statement relating to an offering for its own account
or the account of others under the Securities Act of any of its equity
securities, other than on Form S-4 or Form S-8 (each as promulgated under the
Securities Act) or their then equivalents relating to equity securities to be
issued solely in connection with any acquisition of any entity or business or
equity securities issuable in connection with stock option or other employee
benefit plans, then the Company shall send to each Holder written notice of such
determination and, if within fifteen days after receipt of such notice, any such
Holder shall so request in writing, the Company shall include in such
registration statement all or any part of such Registrable Securities such
holder requests to be registered.

(aa) Amendments and Waivers. The provisions of this Agreement, including the
provisions of this sentence, may not be amended, modified or supplemented, and
waivers or consents to departures from the provisions hereof may not be given,
unless the same shall be in writing and signed by the Company and the Holders of
at least two-thirds of the then outstanding Registrable Securities.
Notwithstanding the foregoing, a waiver or consent to depart from the provisions
hereof with respect to a matter that relates exclusively to the rights of
Holders and that does not directly or indirectly affect the rights of other
Holders may be given by Holders of at least a majority of the Registrable
Securities to which such waiver or consent relates; provided, however, that the
provisions of this sentence may not be amended, modified, or supplemented except
in accordance with the provisions of the immediately preceding sentence.

(bb) Notices. Any and all notices or other communications or deliveries required
or permitted to be provided hereunder shall be in writing and shall be deemed
given and effective on the earliest of (i) the date of transmission, if such
notice or communication is delivered via facsimile at the facsimile telephone
number specified in this Section prior to 6:30

<PAGE>

p.m. (New York City time) on a Business Day, (ii) the Business Day after the
date of transmission, if such notice or communication is delivered via facsimile
at the facsimile telephone number specified in the Purchase Agreement later than
6:30 p.m. (New York City time) on any date and earlier than 11:59 p.m. (New York
City time) on such date, (iii) the Business Day following the date of mailing,
if sent by nationally recognized overnight courier service, or (iv) upon actual
receipt by the party to whom such notice is required to be given. The address
for such notices and communications shall be as follows: If to the Company:
SafeScience, Inc. Park Square Building 31 St. James Avenue, 8th Floor Boston, MA
02116 Fax: 617-422-0675 Attn: John Burns Chief Financial Officer

         With copies to:            McDermott Will & Emery
                                    50 Rockefeller Plaza
                                    New York, NY  10020-1605
                                    Facsimile No.:   212-547-5444
                                    Attn: Cheryl Reicin, Esq.

         If                         to a Purchaser: To the
                                    address set forth under
                                    such Purchaser's name on
                                    the signature pages hereto.

         If to any other Person who is then the registered Holder:

                                    To the address of such Holder as it appears
                                    in the stock transfer books of the Company

or such other address as may be designated in writing hereafter, in the same
manner, by such Person.

(cc) Successors and Assigns. This Agreement shall inure to the benefit of and be
binding upon the successors and permitted assigns of each of the parties and
shall inure to the benefit of each Holder. The Company may not assign its rights
or obligations hereunder without the prior written consent of each Holder. Each
Holder may assign their respective rights hereunder in the manner and to the
Persons as permitted under the Purchase Agreement.

(dd) Counterparts. This Agreement may be executed in any number of counterparts,
each of which when so executed shall be deemed to be an original and, all of
which taken together shall constitute one and the same Agreement. In the event
that any signature is delivered by facsimile transmission, such signature shall
create a valid binding obligation of the party executing (or on whose behalf
such signature is executed) the same with the same force and effect as if such
facsimile signature were the original thereof.

(ee) Governing Law. All questions concerning the construction, validity,
enforcement and interpretation of this Agreement shall be governed by and
construed and enforced in accordance with the internal laws of the State of New
York, without regard to the principles of conflicts of law thereof. Each party
hereby irrevocably submits to the exclusive

<PAGE>

jurisdiction of the state and federal courts sitting in the City of New York,
borough of Manhattan, for the adjudication of any dispute hereunder or in
connection herewith or with any transaction contemplated hereby or discussed
herein, and hereby irrevocably waives, and agrees not to assert in any suit,
action or proceeding, any claim that it is not personally subject to the
jurisdiction of any such court, that such suit, action or proceeding is
improper. Each party hereby irrevocably waives personal service of process and
consents to process being served in any such suit, action or proceeding by
mailing a copy thereof to such party at the address in effect for notices to it
under this Agreement and agrees that such service shall constitute good and
sufficient service of process and notice thereof. Nothing contained herein shall
be deemed to limit in any way any right to serve process in any manner permitted
by law.

(ff) Cumulative Remedies. The remedies provided herein are cumulative and not
exclusive of any remedies provided by law.

(gg) Severability. If any term, provision, covenant or restriction of this
Agreement is held by a court of competent jurisdiction to be invalid, illegal,
void or unenforceable, the remainder of the terms, provisions, covenants and
restrictions set forth herein shall remain in full force and effect and shall in
no way be affected, impaired or invalidated, and the parties hereto shall use
their reasonable efforts to find and employ an alternative means to achieve the
same or substantially the same result as that contemplated by such term,
provision, covenant or restriction. It is hereby stipulated and declared to be
the intention of the parties that they would have executed the remaining terms,
provisions, covenants and restrictions without including any of such that may be
hereafter declared invalid, illegal, void or unenforceable.

(hh) Headings. The headings in this Agreement are for convenience of reference
only and shall not limit or otherwise affect the meaning hereof.

(ii) Shares Held by the Company and its Affiliates. Whenever the consent or
approval of Holders of a specified percentage of Registrable Securities is
required hereunder, Registrable Securities held by the Company or its Affiliates
(other than any Holder or transferees or successors or assigns thereof if such
Holder is deemed to be an Affiliate solely by reason of its holdings of such
Registrable Securities) shall not be counted in determining whether such consent
or approval was given by the Holders of such required percentage.

(jj) Independent Nature of Purchasers' Obligations and Rights. The obligations
of each Purchaser hereunder is several and not joint with the obligations of any
other Purchaser hereunder, and neither Purchaser shall be responsible in any way
for the performance of the obligations of any other Purchaser hereunder. Nothing
contained herein or in any other agreement or document delivered at any closing,
and no action taken by any Purchaser pursuant hereto or thereto, shall be deemed
to constitute the Purchasers as a partnership, an association, a joint venture
or any other kind of entity, or create a presumption that the Purchasers are in
any way acting in concert with respect to such obligations or the transactions
contemplated by this Agreement. Each Purchaser shall be entitled to protect and
enforce its rights, including without limitation the rights arising out of this
Agreement, and it shall not be necessary for any other Purchaser to be joined as
an additional party in any proceeding for such purpose.

                  [REMAINDER OF PAGE INTENTIONALLY LEFT BLANK
                           SIGNATURE PAGES TO FOLLOW]

<PAGE>

         IN WITNESS WHEREOF, the parties have executed this Registration Rights
Agreement as of the date first written above.

                                           SAFESCIENCE, INC.

                                           By:__________________________________
                                                Name:
                                                Title:

                   [REMAINDER OF PAGE INTENTIONALLY LEFT BLANK
                     SIGNATURE PAGES OF PURCHASER TO FOLLOW]

<PAGE>

                         STRONG RIVER INVESTMENTS, INC.

                                       By:_____________________________________
                                            Name:  Miriam O. Hyman
                                            Title:   Attorney-in-Fact

                                       Address for Notice:

                         Strong River Investments, Inc.
                                        c/o Gonzalez-Ruiz & Aleman (BVI) Limited
                                        Wickhams Cay I, Vanterpool Plaza
                                        P.O. Box 873
                            Road Town, Tortolla, BVI

                                            With copies to:

                                         Robinson Silverman Pearce Aronsohn
                                         & Berman LLP
                                         1290 Avenue of the Americas
                                         New York, NY 10104
                                         Facsimile No.:  (212) 541-4630 and
                                         (212) 541-1432
                                         Attn: Kenneth L. Henderson, Esq. and
                                         Eric L. Cohen, Esq.

<PAGE>

                            MONTROSE INVESTMENTS LTD.

                                            By:_________________________________
                                                 Name:
                                                 Title:

                                            Address for Notice:

                                            Montrose Investments Ltd.
                                            300 Crescent Court, Suite 700
                                            Dallas, TX 75201
                                            Facsimile: (214) 758-1221
                                            Attn:    Will Rose
                                                     Kim Rozman

                                            With copies to:

                                            Robinson Silverman Pearce Aronsohn
                                            & Berman LLP
                                            1290 Avenue of the Americas
                                            New York, NY 10104
                                            Facsimile No.:  (212) 541-4630 and
                                            (212) 541-1432
                                            Attn:    Kenneth L. Henderson, Esq.
                                                     Eric L. Cohen, Esq.

<PAGE>

                                                                         Annex A
                                                                         -------

                              PLAN OF DISTRIBUTION
                              --------------------

         The Selling Stockholders and any of their pledgees, assignees and
successors-in-interest may, from time to time, sell any or all of their shares
of Common Stock on any stock exchange, market or trading facility on which the
shares are traded or in private transactions. These sales may be at fixed or
negotiated prices. The Selling Stockholders may use any one or more of the
following methods when selling shares:

$        ordinary brokerage transactions and transactions in which the broker-
         dealer solicits purchasers;

$        block trades in which the broker-dealer will attempt to sell the shares
         as agent but may position and resell a portion of the block as
         principal to facilitate the transaction;

$        purchases by a broker-dealer as principal and resale by the broker-
         dealer for its account;

$        an exchange distribution in accordance with the rules of the applicable
         exchange;

$        privately negotiated transactions;

$        broker-dealers may agree with the Selling Stockholders to sell a
         specified number of such shares at a stipulated price per share;

$        a combination of any such methods of sale; and

$        any other method permitted pursuant to applicable law.

         The Selling Stockholders may also sell shares under Rule 144 under the
Securities Act, if available, rather than under this prospectus.

         Broker-dealers engaged by the Selling Stockholders may arrange for
other brokers-dealers to participate in sales. Broker-dealers may receive
commissions or discounts from the Selling Stockholders (or, if any broker-dealer
acts as agent for the purchaser of shares, from the purchaser) in amounts to be
negotiated. The Selling Stockholders do not expect these commissions and
discounts to exceed what is customary in the types of transactions involved.

         The Selling Stockholders and any broker-dealers or agents that are
involved in selling the shares may be deemed to be "underwriters" within the
meaning of the Securities Act in connection with such sales. In such event, any
commissions received by such broker-dealers or agents and any profit on the
resale of the shares purchased by them may be deemed to be underwriting
commissions or discounts under the Securities Act.

         The Company is required to pay all fees and expenses incident to the
registration of the shares, including up to $7,500 of the fees and disbursements
of counsel to the Selling Stockholders. The Company has agreed to indemnify the
Selling Stockholders against certain losses, claims, damages and liabilities,
including liabilities under the Securities Act.STRONG RIVER INVESTMENTS, INC.
                    C/O GONZALEZ-RUIZ & ALEMAN (BVI) LIMITED
                        WICKHAMS CAY I, VANTERPOOL PLAZA
                                  P.O. BOX 873
                           ROAD TOWN, TORTOLLA. B.V.I.

                            MONTROSE INVESTMENTS LTD.
                          300 CRESCENT COURT, SUITE 700
                                DALLAS, TX 75201

                                                                  March 29, 2000

SafeScience, Inc.
Park Square Building
31 St. James Avenue, 8th Floor
Boston, MA 02116
Attention: President

         Re:      SafeScience, Inc. (the "Company").
                  ----------------------------------

Gentlemen:

                  Reference is made to the Securities Purchase Agreement (the
"Purchase Agreement"), of even date hereof, between the Company and the
undersigned (the "Purchasers"), pursuant to which the Company will issue and
sell to the Purchasers (i) up to 484,429 shares of Common Stock (the "Initial
Shares"), (ii) Common Stock purchase warrants, each in the form of Exhibit A to
the Purchase Agreement, pursuant to which the holder thereof shall have the
right, under certain circumstances described therein, to acquire shares of
Common Stock upon the terms set forth therein (the "Initial Adjustable Warrant")
and (iii) Common Stock purchase warrants, each in the form of Exhibit B to the
Purchase Agreement, pursuant to which the holder thereof shall have the right,
under certain circumstances described therein, to acquire shares of Common Stock
upon the terms set forth therein (the "Initial Closing Warrants" and together
with the Initial Adjustable Warrants, the "Initial Warrants"), for an aggregate
purchase price of up to $7,000,000. Capitalized terms used and not otherwise
defined in this letter that are defined in the Purchase Agreement shall have the
meanings set forth in the Purchase Agreement. The Initial Warrants and the
Initial Shares are sometimes collectively referred to herein as the "Initial
Securities."

                  The Purchasers shall, severally and not jointly, commit,
subject to and upon the terms and conditions hereof, to purchase from the
Company, and the Company shall sell to the Purchasers on the Additional Closing
Date (as defined herein): (i) up to [ ] 1

--------
1 The number which equals $7,000,000 divided by the lesser of (i) 110% of the
average of the Per Share Market Values for the four Trading Days preceding the
Additional Closing Date and (ii) $16.00 (subject to equitable adjustment for
stock splits, recombinations and similar events).

<PAGE>

shares of Common Stock (the "Additional Shares"), (ii) additional Initial
Adjustable Warrants (the "Additional Adjustable Warrants") and (iii) additional
Initial Closing Warrants pursuant to which the holders thereof shall have the
right at any time and from time to time thereafter through the fifth anniversary
of the Additional Closing Date (as defined herein) to acquire an aggregate of up
to [ ] 2 shares of Common Stock (the "Additional Closing Warrants and together
with the Additional Adjustable Warrants, the "Additional Warrants"), for an
aggregate purchase price of $7,000,000 (the "Additional Purchase Price"),
provided, that if the Additional Purchase Price shall exceed 6% of the market
capitalization of the Common Stock on the Additional Closing Date, the
Additional Closing (as defined herein) shall not take place. The Additional
Shares and Additional Warrants are collectively referred to herein as the
"Additional Securities."

                  The commitment of the Purchasers set forth in this letter is
subject to the terms, conditions and qualifications set forth below:

Form of Additional Adjustable Warrants. The Additional Adjustable Warrants shall
be identical to the Initial Adjustable Warrants except that the Purchase Price
applicable thereto shall equal the lesser of (i)110% of the average of the Per
Share Market Values for the four Trading Days preceding the Additional Closing
Date and (ii) $16.00 (subject to equitable adjustment for stock splits,
recombinations and similar events).

2. Form of Additional Closing Warrants. The Additional Closing Warrants shall be
identical to the Initial Closing Warrants except that the Exercise Price (as
defined in the Initial Closing Warrants) shall be equal to 120% of the average
of the closing bid prices of the Common Stock for the five (5) Trading Days
immediately preceding the Additional Closing Date.

3. Additional Documentation. In order to effectuate a purchase and sale of the
Additional Securities, prior to their issuance, the Company and the Purchasers
shall enter into the following agreements: (a) a securities purchase agreement
identical to the Purchase Agreement, mutatis mutandis (the "Additional Purchase
Agreement") and (b) a registration rights agreement identical to the
Registration Rights Agreement, mutatis mutandis (the "Additional Registration
Rights Agreement", and together with the Additional Purchase Agreement, the
Additional Warrants, collectively the "Additional Transaction Documents"). The
Purchasers shall prepare the Additional Transaction Documents.

4. Additional Closing. (i) Each Purchaser and the Company shall each have the
right to deliver a written notice to the other (the "Additional Financing
Notice") requiring such other party to either sell or buy (severally and not
jointly), as the case may be, the Additional Securities for the Additional
Purchase Price. The Additional Financing Notice may be delivered no earlier than
190 days following the Closing Date and no later than 210 days following the
Closing Date, or as otherwise agreed to by the parties hereto. At the Additional
Closing each Purchaser which receives or delivers an Additional Closing

------
2 The number which equals 7.5% of $7,000,000 divided by the lesser of (i) 110%
of the average of the Per Share Market Values for the four Trading Days
preceding the Additional Closing Date and (ii) $16.00 (subject to equitable
adjustment for stock splits, recombinations and similar events).

<PAGE>

Notice pursuant to the terms hereof shall (subject to the terms and conditions
herein) purchase such portion of the Additional Securities as equals such
Purchaser's pro-rata portion of the Initial Securities issued and sold at the
Closing. The closing of the purchase and sale of Additional Securities (the
"Additional Closing") shall take place at the offices of Robinson Silverman,1290
Avenue of the Americas, New York, New York 10104, on the fifth (5th) Business
Day after the Additional Financing Notice is received by a Purchaser or the
Company, as the case may be, or on such other date as otherwise agreed to by the
parties hereto, provided, that in no case shall the Additional Closing take
place unless and until all of the conditions listed in Section 5 of this letter
shall have been satisfied by the Company or waived by the Purchasers. The date
of the Additional Closing is hereinafter referred to as the "Additional Closing
Date." Notwithstanding anything to the contrary contained in this letter, each
Purchaser may, prior to the Additional Closing Date, designate an Affiliate
thereof to acquire all or any portion of the Additional Securities.

         (i) At the Additional Closing, the parties shall deliver or shall cause
to be delivered the following: (a) the Company shall deliver to (x) each
Purchaser which receives or delivers an Additional Closing Notice pursuant to
the terms hereof or its designated Affiliate: (1) the number of Additional
Shares purchased equal to such Purchaser's pro rata portion of the Initial
Shares issued and sold at the Closing, registered in the name of such Purchaser
or its designated Affiliate, (2) an Additional Adjustable Warrant registered in
the name of such Purchaser or its designated Affiliate, (3) an Additional
Closing Warrant registered in the name of such Purchaser or its designated
Affiliate, entitling the holder thereof to purchase such number of shares of
Common Stock as equals such Purchaser's pro-rata portion of the shares of Common
Stock underlying the Initial Closing Warrant issued and sold at the Closing to
such Purchaser, (4) a legal opinion in form and substance acceptable to the
Purchasers, (5) an officer's certificate pursuant to Section 5(b) hereof and (6)
executed Additional Transaction Documents and the Transfer Agent Instructions
relating to the Additional Securities, and (y) Robinson Silverman, $20,000 for
the legal fees and expenses incurred by the Purchasers to prepare the Additional
Transaction Documents, which amount shall be deducted by the Purchasers from the
Additional Purchase Price and shall be paid directly to Robinson Silverman and
(b) each Purchaser which receives or delivers an Additional Closing Notice
pursuant to the terms hereof shall deliver to the Company (1) its pro rata
portion of the Additional Purchase Price, in United States dollars in
immediately available funds by wire transfer to an account designated in writing
by the Company for such purpose prior to the Additional Closing Date and (2) the
executed Additional Transaction Documents.

5. Conditions precedent to the Additional Closing. Notwithstanding anything to
the contrary contained in this letter, the commitment of a Purchaser to purchase
the Additional Securities is subject to the satisfaction or waiver by such
Purchaser of each of the following conditions:

     (a) Closing of Initial Shares and Initial Warrants. The Closing shall have
occurred;

     (b) Accuracy of the Company's Representations and Warranties. The

<PAGE>

representations and warranties of the Company contained in the Purchase
Agreement shall be true and correct as of the date when made and as of the
Additional Closing Date as though made on and as of the Additional Closing Date
(other than representations and warranties which relate to a specific date
(which shall not include representations and warranties relating to the "date
hereof") which representations and warranties shall be true as of such specific
date), as evidenced by an officer's certificate attesting to such effect to be
delivered by the Company to the Purchasers at the Additional Closing Date;

     (c) Performance by the Company. The Company shall have performed, satisfied
and complied with all covenants, agreements and conditions required by the
Transaction Documents to be performed, satisfied or complied with by the Company
between the Closing Date and the Additional Closing Date and no Event (as
defined in the Registration Rights Agreement ) shall have occurred which has not
been cured to the satisfaction of the Purchasers;

     (d) Underlying Shares Registration Statement. The Underlying Shares
Registration Statement shall have been declared effective under the Securities
Act by the Commission and shall have remained effective at all times, not
subject to any actual or threatened stop order or subject to any actual or
threatened suspension at any time prior to the Additional Closing Date;

     (e) No Injunction. Since the Closing Date, no statute, rule, regulation,
executive order, decree, ruling or injunction shall have been enacted, entered,
promulgated, amended, modified or endorsed by any court of governmental
authority of competent jurisdiction or governmental authority, stock market or
trading facility which prohibits the consummation of any of the transactions
contemplated by the Additional Transaction Documents or makes impracticable the
transactions contemplated thereby;

     (f) Adverse Changes. Since the Closing Date, no event or series of events
which reasonably would be expected to have or result in a Material Adverse
Effect shall have occurred;

     (g) No Suspensions of Trading in Common Stock. The trading in the Common
Stock shall not have been suspended by the Commission or on the NASDAQ at any
time since the Closing Date and the Company shall not have received any notice
of threatened or pending proceedings for delisting the Common Stock from NASDAQ;

     (h) Listing of Common Stock. The Common Stock shall have been at all times
since the Closing Date listed for trading on the NASDAQ;

     (i) Shares of Common Stock. The Company shall have duly reserved the number
of shares of Common Stock as required by the Additional Transaction Documents to
be reserved for issuance upon exercise of the Additional Warrants;

     (j) Performance of Exercise Obligations. The Company shall have timely
complied with its exercise and delivery requirements under the Initial Warrants;

     (k) Closing Threshold. For the ten (10) Trading Days immediately preceding

<PAGE>

the date of the delivery of the Additional Financing Notice, the average daily
trading volume of the Common Stock on the NASDAQ shall be at least 50,000 shares
and the average of the Per Share Market Value for such ten (10) Trading Day
period shall be greater than $10.00 (subject to equitable adjustments for stock
splits, recombinations and similar events);

     (l) Shareholder Approval. No approval of the shareholders of the Company
shall be required under the rules of the Nasdaq Stock Market or such other
exchange or trading facility or which the Common Stock is the traded or listed
for trading in order to issue a minimum of twice the number of the shares of
Common Stock issuable upon exercise of the Additional Adjustable Warrants
(assuming(x) such exercise occurred on the Additional Closing Date (y) the
Applicable Share Number (as defined in the Additional Adjustable Warrants)
relating to each Additional Adjustable Warrant equals 100% of the Additional
Shares and (z) and Adjustment Price (as defined in the Additional Adjustable
Warrants) shall be deemed to mean the average of the four lowest Per Share
Market Values (which need not occur on consecutive Trading Days) during the 40
consecutive Trading Days preceding the Additional Closing Date); and

     (m) Deliveries pursuant to the Additional Transaction Documents. At the
Additional Closing, the Company shall deliver the Additional Securities and
executed Additional Transaction Documents and Transfer Agent Instructions
relating to the Additional Securities in the forms contemplated by this letter.

6.  Independent Nature of Purchasers' Obligations and Rights. The obligations of
each Purchaser hereunder is several and not joint with the obligations of any
other Purchaser hereunder, and neither Purchaser shall be responsible in any way
for the performance of the obligations of any other Purchaser hereunder. Nothing
contained herein or in any other agreement or document delivered at any closing,
and no action taken by any Purchaser pursuant hereto or thereto, shall be deemed
to constitute the Purchasers as a partnership, an association, a joint venture
or any other kind of entity, or create a presumption that the Purchasers are in
any way acting in concert with respect to such obligations or the transactions
contemplated by this Agreement. Each Purchaser shall be entitled to protect and
enforce its rights, including, without limitation, the rights arising out of
this letter or out of the Additional Transaction Documents, if any, and it shall
not be necessary for any other Purchaser to be joined as an additional party in
any proceeding for such purpose.

7. Governing Law. This letter shall be governed by and construed and enforced in
accordance with the internal laws of the State of New York, without regard to
the principles of conflicts of law thereof.

8. Execution. This letter may be executed in two or more counterparts, all of
which when taken together shall be considered one and the same agreement and
shall become effective when counterparts have been signed by each party and
delivered to the other party, it being understood that both parties need not
sign the same counterpart. In the event that any signature is delivered by
facsimile transmission, such signature shall create a valid and binding
obligation of the party executing (or on whose behalf such signature is
executed) the same with the same force and effect as if such facsimile signature
page were an original thereof.

<PAGE>

                  Please indicate your agreement with the foregoing by executing
a countersigned copy of this letter and returning the same to our attention,
whereupon effective immediately thereafter this letter shall become a legally
valid and binding agreement between the Purchasers and the Company.

                  We look forward to our continuing relationship.

                  Sincerely,

                  Strong River Investments, Inc.

                  By:    _______________________
                         Name: Miriam O. Hyman
                         Title: Attorney-in-Fact

                  Montrose Investments Ltd.

                  By:    _______________________
                         Name:
                         Title:

Agreed and accepted
March 29, 2000

SafeScience, Inc.

By:    _______________________
       Name:
       Title:

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