EXHIBIT 4.6

                          REGISTRATION RIGHTS AGREEMENT

           THIS REGISTRATION  RIGHTS AGREEMENT (this  "Agreement"),  dated as of
March  23,  1999,  is by and  between  Sepracor  Inc.,  a  Delaware  corporation
("Sepracor"), and HemaSure Inc., a Delaware corporation (the "Company").

                              PRELIMINARY STATEMENT

           WHEREAS,  pursuant to a  Securities  Purchase  Agreement of even date
herewith  (the  "Securities  Purchase  Agreement")  by and  between  the parties
hereto,  the  Company  issued and granted to Sepracor  (i)  1,333,334  shares of
common stock,  par value $.01 per share ("Common  Stock"),  of the Company,  and
(ii) warrants to purchase 667,000 shares of Common Stock; and

           WHEREAS,  the  Company  and  Sepracor  desire to provide  for certain
arrangements  with  respect to the  registration  of such shares of Common Stock
(the "Shares") under the Securities Act of 1933, as amended.

           NOW THEREFORE, in consideration of these premises, and the respective
promises and covenants contained herein, the parties hereto agree as follows:


                                   ARTICLE 1.

                                   DEFINITIONS

           Section  1.1 Certain  Definitions.  For  purposes of this  Agreement,
capitalized  terms used herein and not defined  elsewhere  herein shall have the
following meanings:

           "Act" means the United States Securities Act of 1933, as amended,  or
any similar  Federal  statute,  and the rules and  regulations of the Commission
issued under the Act, as they each may, from time to time, be in effect.

           "Commission"   means  the  United  States   Securities  and  Exchange
Commission, or any other Federal agency at the time administering the Act.

           "Common Stock" means the shares of common stock,  par value $0.01 per
share, of the Company.

           "Exchange  Act" means the United  States  Securities  Exchange Act of
1934, as amended, or any similar Federal statute,  and the rules and regulations
of the Commission  issued under the Exchange Act, as they each may, from time to
time, be in effect.


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           "Indemnified  Party" has the  meaning  described  in  Section  2.4(c)
below.

           "Indemnifying  Party" has the  meaning  described  in Section  2.4(c)
below.

           "Registration  Statement" means a registration statement filed by the
Company  with the  Commission  for a  public  offering  and  sale of its  equity
securities  (other  than a  registration  statement  on Form S-8 or Form S-4, or
their successors,  or any other form for a limited purpose,  or any registration
statement  covering  only  securities  proposed  to be  issued in  exchange  for
securities or assets of another corporation).

           "Registration Expenses" means all expenses incurred by the Company in
complying with Section 2.1 and Section 2.2, including,  without limitation,  all
registration and filing fees, exchange listing fees, printing expenses, fees and
disbursements of counsel for the Company,  state Blue Sky fees and expenses, and
the  expense  of  any  special  audits  incident  to or  required  by  any  such
registration,  but excluding  underwriting  discounts on the Registrable Shares,
selling commissions on the Registrable  Shares,  transfer taxes and the fees and
expenses of any selling Stockholders',  including such selling Stockholders' own
counsel, which shall be borne by the participating Stockholders in proportion to
the number of Registrable Shares offered by each.

           "Registrable  Shares" means (i) the Shares, and (ii) any other shares
of Common  Stock  issued in respect  thereof  (because  of stock  splits,  stock
dividends,  reclassifications,  recapitalizations, or similar events); provided,
that  shares of Common  Stock  which are  Registrable  Shares  shall cease to be
Registrable  Shares  (i) when they  have been  sold,  transferred  or  otherwise
disposed of or exchanged  pursuant to a  registration  statement  under the Act,
(ii) when such shares are eligible  for resale  pursuant to Rule 144 (k) (or its
successor) or in single  transaction  pursuant to Rule 144(e) (or its successor)
under the Act,  or (iii) upon any sale,  transfer  or other  disposition  in any
manner  to any  person  or  entity  which,  by  virtue  of  Section  2.9 of this
Agreement, is not entitled to the rights provided by this Agreement.

           "Stockholders"  means Sepracor and any person or entities to whom the
rights  granted under this Agreement are validly  transferred  by Sepracor,  and
their permitted successors or assigns pursuant to Section 2.9 hereof.


                                   ARTICLE 2.

                               REGISTRATION RIGHTS

           Section 2.1 Required Registrations.

                     (a)  Commencing  on  the  date  hereof,  a  Stockholder  or
Stockholders  may request,  in writing  (which request shall state the number of
Registrable Shares to be so registered,  the intended method of distribution and
a certification as to the market value of such shares as


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described below), that the Company effect the registration of Registrable Shares
owned by such Stockholder or Stockholders  having an aggregate offering price of
at least $1,000,000  (based on the last reported sale price for the Common Stock
on the business day preceding the date of such written  request,  as reported by
the OTC Bulletin Board or any other exchange or market on which the Common Stock
is then listed or included for quotation). Upon receipt of any such request, the
Company shall within 10 days give written  notice of such proposed  registration
to all Stockholders.  Such Stockholders  shall have the right, by giving written
notice to the Company within 30 days after the Company  provides its notice,  to
elect to have included in such registration such of their Registrable  Shares as
such  Stockholders may request in such notice of election;  provided that if the
underwriter (if any) managing the offering determines that, because of marketing
factors,  all  of the  Registrable  Shares  requested  to be  registered  by all
Stockholders may not be included in the offering, then all Stockholders who have
requested registration shall participate in the registration pro rata based upon
the number of Registrable  Shares which they have requested to be so registered,
provided,  however,  that the number of Registrable  Shares shall not be reduced
unless all securities  that are not  Registrable  Shares are first excluded from
the  underwriting.  Thereupon,  the Company shall file a Registration  Statement
under the Act, to the extent  necessary to permit the sale or other  disposition
of the subject  Registrable  Shares in  accordance  with the intended  method of
distribution specified in the written registration request.

                    (b) The  Company  shall not be  required to effect more than
two (2) registrations  pursuant to paragraph (a) above. In addition, the Company
shall not be required  to effect any  registration  within six months  after the
effective date of any other Registration Statement registering shares to be sold
by the Company.

                    (c) If at any  time  any  request  to  register  Registrable
Shares  pursuant to this  Section 2 is received by the  Company,  the Company is
engaged in, or the Board of  Directors  of the Company has  resolved to initiate
within 30 days of the time of the request for a registration as provided in this
Section  2, a  registered  public  offering  as to which  the  Stockholders  are
entitled to include Registrable Shares pursuant to Section 2.2, or is engaged in
any  activity  other  than  such a public  offering  which,  in the  good  faith
determination of the Company's Board of Directors, would be materially adversely
affected  by the  requested  registration,  then the  Company  may at its option
direct that such  request be delayed for a period not in excess of 120 days from
(i) the earlier of (1) the effective  date of such offering and (2) the 60th day
after the  filing of such  offering,  or (ii) the date of  commencement  of such
other material activity, as the case may be, such right to delay a request to be
exercised by the Company not more than once in any consecutive 12-month period.

           Section 2.2  Incidental Registration.

           (a) Whenever the Company proposes to file a Registration Statement at
any time and from time to time  (including,  to the  extent  the  Company  is so
permitted,  a registration  effected by the Company for stockholders  other than
the Stockholder (a "Registration"),  it will, prior to such filing, give written
notice to all  Stockholders  of its  intention  to do so and,  upon the  written
request


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of a Stockholder or Stockholders given within 10 days after the Company provides
such notice (which  request shall state the number of  Registrable  Shares to be
registered and the intended method of distribution of such Registrable  Shares),
the Company shall, subject to Section 2.2(b) below, cause all Registrable Shares
which the Company has been requested by such  Stockholder or  Stockholders to be
included in the Registration;  provided that the Company shall have the right to
postpone or withdraw  any  registration  effected  pursuant to this  Section 2.2
without obligation or liability to any Stockholder.

           (b) In  connection  with any  Registration  under  this  Section  2.2
involving an underwritten offering, the Company shall not be required to include
any Registrable  Shares in such  Registration  unless the holders thereof accept
the terms of the  underwriting  as  agreed  upon  between  the  Company  and the
underwriters  selected  by it. If in the  opinion  of the  managing  underwriter
employed by the  Company  for the  distribution  of equity  securities  it shall
determine, in its sole discretion, that the registration of all, or part of, the
Registrable  Shares  which the  holders  have  requested  to be  included  would
interfere with the successful  marketing of the proposed public  offering,  then
the Company shall be required to include in the Registration only that number of
Registrable Shares, if any, which the managing  underwriter believes may be sold
without  interfering  with  the  successful  marketing  of the  proposed  public
offering.  If the number of Registrable Shares to be included in Registration in
accordance  with the foregoing is less than the total number of shares which the
holders of Registrable Shares have requested to be included, then the holders of
Registrable  Shares  who  have  requested  registration  and  other  holders  of
securities  entitled to include them in such  Registration  shall participate in
the underwritten offering pro rata based upon their total ownership of shares of
Common  Stock of the  Company.  If any holder  would thus be entitled to include
more shares than such holder  requested  to be  registered,  the excess shall be
allocated  among  other  requesting  holders  pro rata based  upon  their  total
ownership of shares of Common Stock of the Company.

           Section 2.3  Registration Procedures.

           (a) If and whenever the Company is required by the provisions of this
Agreement to effect the registration of any of the Registrable  Shares under the
Act, the Company shall:

                   (i) file with the  Commission a  Registration  Statement with
           respect to such Registrable  Shares and use its best efforts to cause
           that  Registration  Statement to become and remain effective for such
           period of time (not  exceeding  three  months) as may be necessary to
           effect  the  sale or  other  disposition  of all  Registrable  Shares
           covered  by such  Registration  Statement  or until  the  Registrable
           Shares covered thereby cease to be Registrable  Shares,  whichever is
           sooner;

                  (ii) as  expeditiously  as possible  prepare and file with the
           Commission  any  amendments  and  supplements  to  the   Registration
           Statement and the prospectus  included in the Registration  Statement
           as may be necessary to keep the Registration  Statement effective for
           the period described in Section 2.3(a)(i) above;


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                 (iii) as  expeditiously  as  possible  furnish to each  selling
           Stockholder  such  reasonable  numbers  of copies of the  prospectus,
           including a preliminary prospectus,  and such other documents as each
           selling Stockholder may reasonably request in order to facilitate the
           public sale or other  disposition of the Registrable  Shares owned by
           such selling Stockholder;

                  (iv) as  expeditiously  as  possible  register  or qualify the
           Registrable  Shares covered by the  Registration  Statement under the
           securities or Blue Sky laws of such states as the selling Stockholder
           shall reasonably  request;  provided,  however,  that (x) the Company
           shall not for any  purpose be required to qualify to do business as a
           foreign  corporation  in  any  jurisdiction  wherein  it  is  not  so
           qualified  or execute a general  consent to service of process in any
           jurisdiction  and (y) if the Company is offering  securities  for its
           own account,  it need not register or qualify under the securities or
           Blue Sky laws of any  jurisdiction in which the managing  underwriter
           has no intention of offering or selling securities for the account of
           the Company  (except  that the Company  will use its best  efforts to
           register  or  qualify  Registrable   Securities  in  such  additional
           jurisdiction as any Stockholder may request subject to the limitation
           of clause (x) and at such Stockholder's expense);

                   (v)  if  the  distribution  is  to be  made  by  means  of an
           underwritten  public  offering  and subject to  receiving  reasonable
           assurances of  confidentiality,  make available for inspection by the
           underwriters  and its counsel or other  advisors,  such financial and
           other information and books and records of the Company, and cause the
           officers,  directors,  employees,  counsel and independent  certified
           public  accountants  of the Company to respond to such  inquiries  as
           shall be reasonably necessary,  in the judgment of such underwriters'
           counsel, to conduct a reasonable  investigation within the meaning of
           Section 11 of the Act; and

                  (vi)  use  best  efforts  to make  available  to its  security
           holders,  as soon as reasonably  practicable,  an earnings  statement
           covering a period of at least twelve  months which shall  satisfy the
           provisions of Section 11(a) of the Act and Rule 158 thereunder.

           (b) Each selling  Stockholder of Registrable Shares agrees that, upon
receipt of any notice from the Company of (i) any request by the  Commission for
amendments or  supplements  to a  Registration  Statement or related  prospectus
covering any of such selling Stockholder's Registrable Shares, (ii) the issuance
by  the  Commission  of  any  stop  order  suspending  the  effectiveness  of  a
Registration  Statement covering any of such selling  Stockholder's  Registrable
Shares or the initiation of any proceedings for that purpose,  (iii) the receipt
by the  Company  of any  notification  with  respect  to the  suspension  of the
qualification  of any  Registrable  Shares for sale in any  jurisdiction  or the
initiation or threatening of any proceeding for such purpose, (iv) the happening
of any event  that  requires  the  making  of any  changes  in the  Registration
Statement covering any of such selling Stockholder's  Registrable Shares so that
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


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make the statements  therein not misleading or that any related  prospectus will
not  contain  any  untrue  statement  of a  material  fact or omit to state  any
material fact necessary in order to make the statements therein, in light of the
circumstances  under which they are made, not misleading,  and (v) the Company's
reasonable  determination  that a  post-effective  amendment  to a  Registration
Statement  covering any of such selling  Stockholder's  Registrable  Shares or a
supplement  to any related  prospectus  is required  under the Act; such selling
Stockholder will forthwith  discontinue  disposition of such Registrable  Shares
until it is advised in writing  by the  Company  that the use of the  applicable
prospectus (as amended or  supplemented,  as the case may be) and disposition of
the Registrable Shares covered thereby pursuant thereto may be resumed provided,
however,  (x) that such selling  Stockholder shall not resume its disposition of
Registrable Shares pursuant to such Registration Statement or related prospectus
unless it has received notice from the Company that such Registration  Statement
or  amendment  has  become  effective  under the Act and has  received a copy or
copies of the related  prospectus (as then amended or supplemented,  as the case
may be) unless the Registrable  Shares are then listed on a national  securities
exchange and the Company has advised such selling  Stockholder  that the Company
has delivered copies of the related prospectus, as then amended or supplemented,
in transactions  effected upon such exchange,  subject to any subsequent receipt
by such  selling  Stockholder  from the  Company  of notice of any of the events
contemplated by Stock clauses (i) through (iv) of this paragraph, and, (y) if so
directed  by the  Company,  such  holder  will  deliver to the  Company  (at the
Company's  expense) all copies,  other than  permanent  file copies then in such
Stockholder's  possession,  of the prospectus  covering such Registrable  Shares
current at the time of receipt of such notice.

           Section  2.4  Allocation  of  Expenses.  The  Company  will  pay  all
Registration Expenses of all Registrations under this Agreement.

           Section 2.5  Indemnification.

           (a) In the event of any Registration of any of the Registrable Shares
under the Act pursuant to this  Agreement,  the Company will  indemnify and hold
harmless the seller of such Registrable  Shares,  and each other person, if any,
who  controls  such  seller  within the meaning of the Act or the  Exchange  Act
against any losses, claims,  damages or liabilities,  joint or several, to which
such seller or controlling person may become subject under the Act, the Exchange
Act,  state  securities or Blue Sky laws or  otherwise,  insofar as such losses,
claims,  damages or liabilities (or actions in respect  thereof) arise out of or
are based  upon any untrue  statement  of any  material  fact  contained  in any
Registration Statement under which such Registrable Shares were registered under
the Act,  any  preliminary  prospectus  or  final  prospectus  contained  in the
Registration  Statement,  or any amendment or  supplement  to such  Registration
Statement,  or arise out of or are based upon the  omission  to state a material
fact required to be stated therein or necessary to make the  statements  therein
not misleading; and, subject to Section 2.5(c) below, the Company will reimburse
such seller and each such controlling person for any legal or any other expenses
reasonably  incurred by such seller or  controlling  person in  connection  with
investigating or defending any such loss,  claim,  damage,  liability or action;
provided,  however,  that the Company will not be liable in any such case to the
extent that any such loss, claim, damage or liability arises


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out  of or is  based  upon  any  untrue  statement  or  omission  made  in  such
Registration Statement,  preliminary prospectus or final prospectus, or any such
amendment  or  supplement,  in  conformity  with  information  furnished  to the
Company,  in writing,  by or on behalf of such seller or controlling  person for
use in the preparation thereof or inclusion therein.

           The indemnity  provisions  in this Section  2.5(a) are subject to the
condition that,  insofar as they relate to any untrue statement or omission made
in a preliminary  prospectus or prospectus but eliminated or remedied in a final
prospectus or an amended or supplemented  prospectus on file with the Commission
at the time the  Registration  Statement  becomes  effective  or any  amended or
supplemented  prospectus  filed with the Commission  pursuant to Rule 424 or any
successor  provision  under the Act (the  "Final  Prospectus"),  such  indemnity
provisions  shall  not  inure  to the  benefit  of any  selling  Stockholder  of
Registrable  Shares (x) if such selling  Stockholder is not selling  Registrable
Shares through an underwriter, if the Company has previously delivered copies of
such Final Prospectus to such selling  Stockholder of Registrable  Shares or, if
Registrable  Shares are then listed on a national  securities  exchange,  if the
Company  has  previously  delivered  copies  of such  Final  Prospectus  to such
national  securities  exchange in accordance with Rule 153 or any successor rule
under the Act, or (y) if such selling  Stockholder is selling Registrable Shares
through an underwriter  or  underwriters,  the Company has previously  delivered
copies of such Final Prospectus to such underwriter or underwriters.

           (b) In the event of any registration of any of the Registrable Shares
under the Act pursuant to this  Agreement,  each seller of  Registrable  Shares,
severally and not jointly, will indemnify and hold harmless the Company, each of
its directors and officers and each  underwriter  (if any), and each person,  if
any, who controls the Company or any such underwriter  within the meaning of the
Act or the Exchange Act,  against any losses,  claims,  damages or  liabilities,
joint or several, to which the Company, such directors and officers, underwriter
or  controlling  person may become  subject under the Act,  Exchange Act,  state
securities  or Blue Sky  laws or  otherwise,  insofar  as such  losses,  claims,
damages or liabilities (or actions in respect thereof) arise out of or are based
upon any untrue  statement  of a material  fact  contained  in any  Registration
Statement under which such Registrable Shares were registered under the Act, any
preliminary  prospectus  or  final  prospectus  contained  in  the  Registration
Statement,  or any  amendment or supplement to the  Registration  Statement,  or
arise out of or are based upon any omission to state a material fact required to
be stated therein or necessary to make the statement therein not misleading,  if
the statement or omission was made in conformity with  information  furnished in
writing to the Company by or on behalf of such seller,  specifically  for use in
connection with the preparation of or inclusion in such Registration  Statement,
prospectus,  amendment or  supplement;  and shall  reimburse  the  Company,  its
directors and officers,  and each such controlling person for any legal or other
expenses  reasonably incurred by any of them in connection with investigation or
defending any such loss, claim, damage, liability or action, provided,  however,
in no event shall any Stockholder's indemnification obligations hereunder exceed
the gross proceeds (less any underwriting  discounts and  commissions)  from the
sale of Registrable  Shares by such Stockholder.  This indemnity shall remain in
full force and effect for the applicable statute of limitation period


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regardless  of any  investigation  made by or on behalf of the  Company  or such
controlling person and shall survive the transfer of shares.

           (c) Each party  entitled to  indemnification  under this  Section 2.5
(the  "Indemnified  Party")  shall give notice to the party  required to provide
indemnification (the "Indemnifying Party") promptly after such Indemnified Party
has actual knowledge of any loss, claim, action, damage or liability as to which
indemnity may be sought,  and shall permit the  Indemnified  Party to assume the
defense of any such claim or any litigation resulting therefrom;  provided, that
counsel for the Indemnifying  Party, who shall conduct the defense of such claim
or litigation,  shall be approved by the Indemnified Party (whose approval shall
not be unreasonably withheld);  and, provided,  further, that the failure of any
Indemnified  Party to give  notice as  provided  herein  shall not  relieve  the
Indemnified  Party of its  obligations  under this  Section  2.5,  except to the
extent that such failure to give notice  prejudices  the  Indemnifying  Party or
such  Indemnifying  Party is damaged by such delay.  The  Indemnified  Party may
participate in such defense at such party's expense; provided, however, that the
Indemnifying   Party  shall  pay  such  expense  (but  in  no  event  shall  the
Indemnifying  Party be  obligated  to pay the fees and expenses of more than one
counsel  for  the  Indemnified  Party  or  Parties)  if  representation  of such
Indemnified  Party by the counsel  retained by the  Indemnifying  Party would be
inappropriate  due to actual or  potential  conflict  of  interests  between the
Indemnified  Party and any  other  party  represented  by such  counsel  in such
proceeding.  No  Indemnifying  Party,  in the  defense  of  any  such  claim  or
litigation shall, except with the consent of each Indemnified Party,  consent to
entry of any judgment or enter into any settlement  which does not include as an
unconditional  term  thereof  the giving by the  claimant or  plaintiff  to such
Indemnified  Party of a release  from all  liability in respect of such claim or
litigation,  and no Indemnified  Party shall consent to entry of any judgment or
settle  such  claim or  litigation  without  the prior  written  consent  of the
Indemnifying Party.

           (d) If  the  indemnification  provided  for in  this  Section  2.5 is
finally determined by a court of competent  jurisdiction to be unavailable to an
Indemnified Party with respect to any loss, liability, claim, damage, or expense
referred to therein or contribution  is required under the Act in  circumstances
for  which   indemnification   is  provided  under  this  Section  2,  then  the
Indemnifying  Party, in lieu of indemnifying  such Indemnified  Party hereunder,
shall  contribute to the amount paid or payable by such  Indemnified  Party as a
result of such loss, liability, claim, damage, or expense (i) in such proportion
as is appropriate to reflect the relative  benefits received by the Indemnifying
Party  on the one  hand and the  Indemnified  Party on the  other or (ii) if the
allocation  provided by clause (i) above is not permitted by applicable  law, in
such  proportion  as is  appropriate  to reflect not only the relative  benefits
received by the Indemnifying  Party on the one hand and the Indemnified Party on
the  other  but  also  the  relative  fault of the  Indemnifying  Party  and the
Indemnified Party as well as any other relevant  equitable  considerations.  The
relative fault of the Indemnifying  Party and of the Indemnified  Party shall be
determined by reference  to, among other  things,  whether the untrue or alleged
untrue  statement of a material  fact or the  omission to state a material  fact
related to information  supplied by the Indemnifying Party or by the Indemnified
Party and the parties' relative intent,  knowledge,  access to information,  and
opportunity to correct or prevent such statement or omission; provided, however,
that, in any such


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case, (A) no Stockholder  will be required to contribute any amount in excess of
the  gross  proceeds  of all  Registrable  Shares  sold by it  pursuant  to such
Registration  Statement,  and (B) no  person  or  entity  guilty  of  fraudulent
misrepresentation,  within the  meaning of  Section  11(f) of the Act,  shall be
entitled  to  contribution  from any  person or entity who is not guilty of such
fraudulent misrepresentation.

           (e)  The  obligations  under  this  Section  2.5  shall  survive  the
completion of any offering of Registrable Shares in a registration statement.

           Section 2.6  Indemnification  with Respect to Underwritten  Offering.
(a) In the event that  Registrable  Shares are sold  pursuant to a  Registration
Statement  in an  underwritten  offering  pursuant to Section  2.2,  the Company
agrees  to  enter   into  an   underwriting   agreement   containing   customary
representations  and  warranties  with respect to the business and operations of
the Company and  customary  covenants  and  agreements  to be  performed  by the
Company,  including  without  limitation  customary  provisions  with respect to
indemnification by the Company of the underwriters of such offering.

           (b) No Stockholder may participate in any  underwritten  registration
pursuant to Section 2 hereunder  unless such  Stockholder (i) agrees to sell the
Registrable  Shares which it proposes to sell in such underwritten  registration
on the basis provided in any underwriting  arrangements  approved by the persons
entitled  hereunder to approve such arrangements and (ii) completes and executes
all questionnaires,  powers of attorney,  reasonable and customary  indemnities,
underwriting  agreements  and other  documents  required under the terms of such
underwriting  arrangements and provides such other information and documentation
as the Company or the  underwriters  may reasonably  request in connection  with
such underwritten registration.

           Section 2.7 Information by Holder.  Each holder of Registrable Shares
included  in any  Registration  shall  furnish to the Company  such  information
regarding  such  holder  and the  distribution  proposed  by such  holder as the
Company may request in writing and as shall be required in  connection  with any
registration, qualification or compliance referred to in this Article 2.

           Section 2.8 "Stand-Off" Agreement. Each Stockholder,  if requested by
the  Company  and an  underwriter  of Common  Stock or other  securities  of the
Company,  shall  agree  not to sell or  otherwise  transfer  or  dispose  of any
Registrable  Shares or other  securities of the Company held by such Stockholder
for a specified  period of time (not to exceed 180 days) following the effective
date of a Registration  Statement;  provided, that all officers and directors of
the Company enter into similar agreements. Such agreement shall be in writing in
a form satisfactory to the Company and such underwriter.  The Company may impose
stop-transfer  instructions  with  respect  to the  Registrable  Shares or other
securities  subject to the foregoing  restriction  until the end of the standoff
period.



810765.2
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<PAGE>



           Section 2.9  Transfer of Rights.

           (a) The rights and  obligations  of Sepracor under this Agreement may
be  transferred  by  Sepracor  to  another  person  or  entity  that  is  then a
stockholder  of the Company,  to any  affiliate of the Company or Sepracor or to
any person or entity acquiring at least 10,000  Registrable  Shares (as adjusted
for stock splits, stock dividends, recapitalization or similar events).

           (b) Any transferee  (other than a stockholder  who is already a party
to an agreement in form and substance  similar to this Agreement) to whom rights
under this  Agreement are  transferred  shall,  as a condition to such transfer,
deliver to the Company a written instrument by which such transferee  identifies
itself,  gives the Company notice of the transfer of such rights,  indicates the
Registrable Shares owned by it and agrees to be bound by the obligations imposed
upon Sepracor under this Agreement.

           (c) A  transferee  to whom  rights are  transferred  pursuant to this
Section 2.9 may not again  transfer  such rights to any other  person or entity,
other than as provided in this Section 2.9.

           Section  2.10  Exchange Act  Registration;  Rule 144  Reporting.  The
Company  covenants  and agrees that until such time as Sepracor no longer  holds
any  Registrable  Shares  (or  such  Registrable  Shares  otherwise  cease to be
Registrable Shares) it will:

           (a)  use its  best  efforts  to  make  and  keep  public  information
available,  as those terms are understood and defined in Rule 144 under the Act,
even  if the  Company  subsequently  ceases  to be  subject  to  such  reporting
requirements; and

           (b) file with the  Commission  in a timely  manner  all  reports  and
documents required of the Company under the Act and the Exchange Act.


                                   ARTICLE 3.

                                  MISCELLANEOUS

           Section 3.1 Notices.  All notices,  requests,  demands,  claims,  and
other communications hereunder shall be in writing. Any notice, request, demand,
claim, or other  communication  hereunder shall be deemed duly delivered two (2)
business days after it is sent by registered or certified  mail,  return receipt
requested,  postage  prepaid,  or one (1)  business  day  after it is sent via a
reputable  nationwide  overnight  courier service,  in each case to the intended
recipient as set forth below:



810765.2
                                       10

<PAGE>



           If to Sepracor:

                   Sepracor Inc.
                   111 Locke Drive
                   Marlborough, MA  01752
                   Facsimile: (508) 357-7495
                   Attention:  Senior Vice President, Finance and Administration

           with a copy to:

                   Hale and Dorr LLP
                   60 State Street
                   Boston, MA  02109
                   Facsimile: (617) 526-5000
                   Attn:  John Chory, Esq.

           If to the Company:

                   HemaSure Inc.
                   140 Locke Drive
                   Marlborough, MA  01752
                   Facsimile: (508) 485-6045
                   Attention:  President and Chief Executive Officer

           with a copy to:

                   Battle Fowler LLP
                   Park Avenue Tower
                   75 East 55th Street
                   New York, NY 10022
                   Facsimile: (212) 856-7816
                   Attention:  Luke P. Iovine, III, Esq.

Either party hereto may hereto give any notice, request,  demand, claim or other
communication  hereunder  using any other means  (including  personal  delivery,
expedited  courier,   messenger  service,  telecopy,  telex,  ordinary  mail  or
electronic  mail),  but  no  such  notice,  request,  demand,  claim,  or  other
communication  shall be  deemed  to have been  duly  given  unless  and until it
actually is received by the  individual  for whom it is  intended.  Either party
hereto may change the address to which notices,  requests,  demands,  claims and
other  communications  hereunder  are to be  delivered by giving the other party
hereto notice in the manner herein set forth.

           Section 3.2 Binding Effect.  This Agreement shall be binding upon and
inure to the benefit of and be  enforceable  by the  respective  successors  and
permitted assigns of the parties hereto.


810765.2
                                       11

<PAGE>



           Section  3.3  Headings.  Article and  Section  headings  used in this
Agreement are for  convenience of reference only and shall not constitute a part
of this Agreement for any purpose or affect the construction of this Agreement.

           Section 3.4 Survival of Agreements,  Representations  and Warranties.
All  agreements,  representations  and warranties  made herein shall survive the
execution and delivery of this Agreement.

           Section 3.5 Amendments and Waivers. Any term of this Agreement may be
amended and the  observance of any term of this  Agreement may be waived (either
generally   or  in  a   particular   instance   and  either   retroactively   or
prospectively),  with the  written  consent of the Company and the holders of at
least  51% of the  Registrable  Shares;  provided,  that this  Agreement  may be
amended with the consent of the holders of less than all Registrable Shares (but
not less than 51% of such shares) only in a manner which affects all Registrable
Shares in the same fashion.  No waivers of or exceptions to any term,  condition
or provision of this Agreement, in any one or more instances, shall be deemed to
be, or construed as, a further or continuing waiver of any such term,  condition
or provision.

           Section 3.6  Governing  Law. This  Agreement  shall be deemed to have
been  made in the  State of New York and the  validity  of this  Agreement,  the
construction,  interpretation  and  enforcement  thereof,  and the rights of the
parties  thereto  shall be  determined  under,  governed  by, and  construed  in
accordance  with the internal laws of the State of New York,  without  regard to
principles of conflicts of law.

           Section 3.7  Arbitration.  Any dispute or controversy  arising under,
out of, in connection with, or in relation to this Agreement shall be determined
and  settled  by  arbitration  in New York by a panel of three  (3)  members  in
accordance with the commercial  rules of the American  Arbitration  Association.
Any award rendered therein shall be final and binding upon the parties and their
legal representatives, successors and assigns and judgment may be entered in any
court having jurisdiction thereof.

           Section 3.8 Execution in Counterparts. This Agreement may be executed
in any number of counterparts and by different parties on separate counterparts,
each of which counterparts,  when so executed and delivered,  shall be deemed to
be an original and all of which counterparts,  taken together,  shall constitute
one and the same  Agreement.  This  Agreement  shall become  effective  upon the
execution of a counterpart hereof by each of the parties hereto.


                         (Signatures on Following Page)



810765.2
                                       12

<PAGE>



           IN WITNESS WHEREOF,  the parties hereto have caused this Agreement to
be executed as of the date first above written.


                                       HEMASURE INC.


                                       By: /s/ James B. Murphy
                                           ------------------------------------
                                       Name:   James B. Murphy
                                       Title:  Senior Vice President of Finance
                                               and Administration

                                       SEPRACOR INC.


                                       By: /s/ Robert Scumaci
                                           ------------------------------------
                                       Name:  Robert Scumaci
                                       Title: Senior Vice President of Finance
                                              and Administration


810765.2

<PAGE>