REGISTRATION AGREEMENT

         This Registration Agreement (the "Registration Agreement") is made and
entered into as of January 29, 1997, between DU PONT CHEMICAL AND ENERGY
OPERATIONS, INC., a Delaware corporation ("DCEO"), E. I. DU PONT DE NEMOURS AND
COMPANY, a Delaware corporation ("DUPONT") and HUDSON TECHNOLOGIES, INC., a New
York corporation ("HTI" or the "Company").

                              W I T N E S S E T H :

         WHEREAS, DCEO, DUPONT and HTI are, simultaneously with this
Registration Agreement, entering into a certain Stock Purchase Agreement ("Stock
Purchase Agreement") to provide a constructive and mutually beneficial
relationship between HTI, DUPONT and DCEO, including the purchase of certain
shares of Common Stock, par value $0.01 per share of HTI.

         NOW, THEREFORE, in consideration of the respective agreements herein
contained and in order to induce DCEO to enter into the Investment Agreement,
the parties agree as follows:

1. DEMAND REGISTRATION

         (a) The demand registration rights of DCEO set forth in Section 1 of
this Registration Agreement may only be exercised by DCEO (i) anytime between
January 29, 1999 and January 29, 2002, and (ii) only one (1) time, after which
such demand registration rights shall terminate.



         (b) Subject to Section l(a), in the event that HTI shall receive a
written request from DCEO that HTI register under the Securities Act of 1933, as
amended (the "Act") on Form S-3, or any other similar form then in effect, and
provided that HTI is eligible to use such Form S-3, at least 500,000 Shares of
Common Stock then owned by DCEO (the "Shares"), HTI agrees that it will use its
best efforts to promptly file (but in no event more than forty-five (45) days
after such request) a registration statement and to cause such registration
statement to become effective as soon as practicable. In the case of any
registration pursuant to this Section 1 which involves a firm commitment
underwritten public offering, the managing underwriter or underwriters shall be
selected by DCEO and approved by HTI, which approval shall not be unreasonably
withheld, and HTI agrees to enter into an underwriting agreement in customary
form with such underwriters. HTI will use its best efforts to cause any such
registration to remain effective (with a prospectus at all times meeting the
requirements of the Act) for 90 days from the effective date of the registration
statement and will use its best efforts to effect such qualifications under
applicable Blue Sky or other state securities laws as may be reasonably
requested by DCEO (provided that HTI shall not be obligated to file a general
consent to service of process or to qualify to do business as a foreign
corporation or to otherwise subject itself to taxation solely for the purpose of
any such qualification) to permit or facilitate such sale or other distribution.
Notwithstanding the above, the Company will not be obligated to 



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undergo an audit of its financial statements other than in the ordinary course
of its business.

         (c) The Company may postpone for up to 60 days the filing or the
effectiveness of a registration statement for a Demand Registration if the
President of the Company delivers a written certificate to DCEO certifying that
the Company's Board of Directors (evidenced by a resolution) has determined that
public disclosure in a Registration Statement of certain information concerning
the Company at that time would materially adversely affect the financial
position or business of the Company; provided that in any such event, DCEO may
withdraw such request and that, if such request is withdrawn, such request will
not be deemed a Demand Registration. The Company may only make one election in
any 12-month period to postpone a Demand Registration pursuant hereto.

2. PIGGYBACK REGISTRATION

         (a) The piggyback registration rights of DCEO set forth in Section 2 of
this Registration Agreement may be exercised by DCEO anytime between January 29,
1998 and January 29, 2002.

         (b) Subject to Section 2(a), if HTI shall take action to register any
of its common stock for sale to the public for cash, it shall promptly give DCEO
written notice of its intention so to do (such notice shall in no event be given
later than five (5) business days after HTI and its underwriter have 




                                      -3-


signed a letter of intent with respect to such offering) and shall use its best
efforts to promptly file (but in no event more than forty-five (45) days after
such request) a registration statement and to cause such registration statement
to become effective as soon as practicable including such number of the Shares
held by DCEO as may be specified by written notice from DCEO delivered to HTI
within fifteen (15) days after receiving the written notice by HTI of its
intention to register; provided, however, that HTI shall not be required to
honor any such request of DCEO unless such request involves registration of at
least 100,000 Shares; provided, however, that if, in the written opinion of the
Company's managing underwriter, if any, for such offering, the inclusion of all
or a portion of the Shares requested to be registered will exceed the maximum
amount of the Company's securities which can be marketed (i) at a price
reasonably related to their then current market value, or (ii) without otherwise
materially adversely affecting the entire offering, then (x) the Company may
exclude from such offering all or a portion of the Shares which it has been
requested to register or (y) if the underwriter so requests, such Shares shall
not be sold until the expiration of 90 days from the effective date of the
offering that gave rise to the piggyback registration rights that are the
subject of this Section 2.

         (c) Notwithstanding the provisions of this Section 2, the Company shall
have the right at any time after it shall have given written notice pursuant to
this Section 2 



                                      -4-


(irrespective of whether any written request for inclusion of Shares shall have
already been made) to elect not to file any such proposed registration
statement, or to withdraw the same after the filing but prior to the effective
date thereof.



                                      -5-


3. PROSPECTUSES, DOCUMENTS, ETC.

         Upon making a request for demand registration pursuant to Section 1
hereof or for piggyback registration pursuant to Section 2 hereof, DUPONT shall
furnish to HTI such information regarding DCEO's holdings and the proposed
manner of distribution thereof as shall be reasonably required in connection
with any registration, qualification or compliance referred to in such Sections,
and shall otherwise reasonably cooperate with HTI in the preparation and filing
of any registration statement, amendment or supplement required thereunder and
in any efforts by HTI to establish any exemptions under federal and state
securities laws. HTI agrees that it will furnish to DUPONT the number of
prospectuses, offering circulars or other documents, or any amendments or
supplements thereto, incident to any registration, qualification or compliance
referred to in Section 1 hereof as DCEO from time to time may reasonably
request.

4. EXPENSES

         The obligations of HTI to register Shares held by DCEO shall be subject
to the following terms and conditions:

         (a) With respect to a demand registration, DUPONT shall pay all
expenses of such registration, including (i) all underwriters' discounts and
commissions, (ii) all expenses (including filing fees) incurred in connection
with qualifying under state securities or Blue Sky laws, (iii) all other filing


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fees, (iv) the cost of any customary insurance policy that the underwriters may,
in the exercise of their sole discretion, require in connection with such
registration, (v) the reasonable fees of HTI's legal counsel, (vi) the fees of
DUPONT's legal counsel, (vii) reasonable audit and other accounting fees and
expenses, and (viii) printing costs (together the "Registration Costs").

         (b) With respect to a piggyback registration, DUPONT shall pay its
proportionate share of all expenses of such registration (the proportion to be
the number of Shares being so registered at DUPONT's request as compared to the
total number of shares of common stock being so registered), including (i) all
underwriters' discounts and commissions in connection with the Shares sold by
DCEO, (ii) its proportionate share of all expenses (including filing fees)
incurred in connection with the qualifying under state securities or Blue Sky
laws, except that with respect to any states requested by DUPONT and not the
underwriters, DUPONT shall pay all expenses incurred in connection with
qualifying under the state securities or Blue Sky laws of such states, (iii) its
proportionate share of all other filing fees, (iv) its proportionate share of
the fees of HTI's legal counsel, (v) all of the fees of DUPONT's legal counsel,
(vi) its proportionate share of audit and other accounting fees and expenses,
and (vii) its proportionate share of printing costs.



                                      -7-


5. INDEMNIFICATION RELATING TO A REGISTRATION STATEMENT

         (a) Whenever pursuant to Section 1 or Section 2 hereof a registration
statement relating to Shares is filed under the Act, HTI will indemnify and hold
harmless DUPONT and DCEO, each underwriter of any such Shares and each person,
if any, who controls any such underwriter, against any losses, claims, damages
or liabilities, joint or several, to which DUPONT and DCEO, any such underwriter
or any such controlling person may become subject under the Act or otherwise,
including any amount paid in settlement of any litigation, commenced or
threatened, if such settlement is effected with the written consent of HTI, and
to reimburse them for all legal or other expenses reasonably incurred by them in
connection with investigating or defending against such loss, claim, damage, or
liability (or actions in respect thereof), insofar as such losses, claims,
damages or liabilities (or actions in respect thereof) arise out of or are based
upon any untrue statement or misrepresentation or alleged untrue statement of a
material fact contained in such registration statement, or preliminary, final or
summary prospectus contained therein, as may be amended or supplemented, or
arise out of or are based upon the omission or alleged omission to state therein
a material fact required to be stated therein or necessary in order to make the
statements therein not misleading, unless such untrue statement or omission was
made in such registration statement or final prospectus in reliance upon and in
conformity with information furnished in writing to the 




                                      -8-


Company in connection therewith by DUPONT or any such underwriter or any such
person through DUPONT or the underwriter expressly for use therein; provided,
however, that the indemnity agreement contained in this Section 5 with respect
to any Preliminary Prospectus will not inure to the benefit of the underwriter
(or to the benefit of any other person that may be indemnified pursuant to this
Section 5 if (A) the person asserting any such losses, claims, damages, expenses
or liabilities purchased the Shares which are the subject thereof from the
underwriter or other indemnified person; (B) the underwriter or other
indemnified person failed to send or give a copy of the Prospectus to such
person at or prior to the written confirmation of the sale of such Shares to
such person; and (C) the Prospectus did not contain any untrue statement or
alleged untrue statement or omission or alleged omission giving rise to such
cause, claim, damage, expense or liability.

         (b) Whenever pursuant to Section 1 or 2 hereof a registration statement
relating to Shares is filed under the Act, DUPONT and DUPONT's underwriter of
the Shares to be registered and each person, if any, who controls any such
underwriter (each such party being referred to severally in this subsection (b)
as the "indemnifying party"), will jointly and severally indemnify and hold
harmless HTI, each of its directors, each of its officers and agents who have
signed such registration statement (including consents) and each other person,
if any, who controls HTI, in the same manner and to the same extent as set forth
in 




                                      -9-


subsection (a) of this Section 5, with respect to any untrue statement or
alleged untrue statement of a material fact contained in such registration
statement, or preliminary, final or summary prospectus contained therein, as may
be amended or supplemented, or with respect to any omission or alleged omission
to state therein a material fact required to be stated therein or necessary to
make the statements therein not misleading, but only if, and to the extent that,
such untrue statement, alleged untrue statement or omission or alleged omission
was made in reliance upon and in conformity with written information furnished
to HTI by an indemnifying party specifically for use in the preparation thereof.

         (c) Promptly after receipt by an indemnified party under subsection (a)
or (b) of this Section 5 of notice of the commencement of any action, such
indemnified party will, if a claim in respect thereof is to be made against the
indemnifying party under such clause, notify the indemnifying party in writing
of the commencement thereof; but the omission so to notify the indemnifying
party will not relieve the indemnifying party from any liability which it may
have to any indemnified party otherwise than under such subsections. In case any
such action shall be brought against any indemnified party, and it shall notify
the indemnifying party of the commencement thereof, the indemnifying party will
be entitled to participate therein, and, jointly with any other indemnifying
party similarly notified, to assume the defense thereof (unless such indemnified
party 



                                      -10-


reasonably objects to such assumption on the ground that there may be
legal defenses available to it which are different from or in addition to those
available to such indemnifying party) with counsel satisfactory to such
indemnified party. After such an assumption, the indemnifying party shall not be
liable to such indemnified party under such subsection for any legal or other
expenses subsequently incurred by such indemnified party in connection with the
defense thereof other than reasonable costs of investigation.

         (d) For purposes of this Section 5 the terms "control", "controlling
person" and "underwriter" have the meanings which they have in and under the
Act.

6. MISCELLANEOUS

         (a) DUPONT, DCEO and HTI acknowledge and agree that irreparable damage
would occur in the event any of the provisions of this Registration Agreement
were not performed in accordance with their specific terms or were otherwise
breached. It is accordingly agreed that the parties shall be entitled to an
injunction or injunctions to prevent breaches of the provisions of this
Registration Agreement and to enforce specifically the terms and provisions
hereof in any court of the United States or any State thereof having
jurisdiction, in addition to any other remedy to which any of them may be
entitled by law or equity.

         (b) All notices, consents, requests, instructions, approvals and other
communications provided for herein and all 



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legal process in regard hereto shall be validly given, made or served, if in
writing and delivered or mailed as provided in the Stock Purchase Agreement.

         (c) This Registration Agreement, the Stock Purchase Agreement, the
Shareholders' Agreement and the Standstill Agreement contain the entire
understanding of the parties with respect to the transactions contemplated
hereby and this Registration Agreement may be amended only by an agreement in
writing executed by the parties hereto.

         (d) For the convenience of the parties, any number of counterparts of
this Registration Agreement may be executed by the parties hereto and each such
executed counterpart shall be, and shall be deemed to be, an original
instrument.

         (e) Descriptive headings are for convenience only and shall not control
or affect the meaning or construction of any provisions of this Registration
Agreement.

         (f) This Registration Agreement shall be binding upon the respective
successors and assigns of DUPONT, DCEO and HTI.

         (g) This Registration Agreement shall be governed by and construed in
accordance with the laws of the State of Delaware applicable to contracts made
and to be performed therein.



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         (h) As used herein the term "person" shall mean any individual,
partnership, corporation, trust or other entity.

7. DEFINITIONS

         Each capitalized term used and not otherwise defined herein shall have
the meaning assigned to it by the Stock Purchase Agreement.

         IN WITNESS WHEREOF, DUPONT, DCEO and HTI have caused this Registration
Agreement to be duly executed by their respective officers, each of whom is duly
authorized, all as of the day and year first above written.



                                    E. I. DUPONT DE NEMOURS AND COMPANY

                                    By
                                    Name:
                                    Title:


                                    DU PONT CHEMICAL AND ENERGY OPERATIONS, INC.

                                    By
                                    Name:
                                    Title:


                                    HUDSON TECHNOLOGIES, INC.

                                    By
                                    Name:
                                    Title: