Exhibit 4.3




                          REGISTRATION RIGHTS AGREEMENT

     REGISTRATION RIGHTS AGREEMENT (the "Agreement"),  dated as of September 15,
1998, by and between  Sepracor Inc., a Delaware  corporation  ("Sepracor"),  and
HemaSure Inc., a Delaware corporation (the "Company").

                              PRELIMINARY STATEMENT

     WHEREAS, pursuant to a Warrant Agreement,  dated September 15, 1998, by and
between the parties  hereto (the  "Warrant  Agreement"),  the Company  issued to
Sepracor  warrants to purchase one million  seven hundred  thousand  (1,700,000)
shares (the  "Shares") of common  stock,  par value $0.01 per share (the "Common
Stock"), of the Company; and

     WHEREAS,   the  Company  and   Sepracor   desire  to  provide  for  certain
arrangements with respect to the registration of 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.

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


728544.4

<PAGE>



     "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  2.10 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 2.10 hereof.


                                   ARTICLE 2.

                               REGISTRATION RIGHTS

     Section 2.1 Required Registrations.

          (a)  Commencing  any time after  September 15, 1999, 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 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
$1,500,000  (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

                                       -2-
728544.4

<PAGE>



to have included in such registration  such of their Registrable  Shares as such
Stockholders  may  request  in  suchnotice  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  one
registration 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) Subject to Section 2.2(c) below,  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 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

                                       -3-
728544.4

<PAGE>



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.

          (c) The  Company  shall not be  required  to effect  more than two (2)
registrations pursuant to paragraph (a) above.

     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;

          (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);


                                       -4-
728544.4

<PAGE>



          (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 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.


                                       -5-
728544.4

<PAGE>



     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 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 related 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

                                       -6-
728544.4

<PAGE>



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  Sepracor's  indemnification
obligations hereunder exceed the gross proceeds (less any underwriting discounts
and commissions) from the sale of Registrable Shares by Sepracor. This indemnity
shall remain in full force and effect for the  applicable  statute of limitation
period  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  in  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 

                                       -7-
728544.4

<PAGE>



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 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 stand-off
period.

     Section 2.9 Termination. [Intentionally Omitted].

     Section 2.10 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, to

                                       -8-
728544.4

<PAGE>



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
2.10 may not again  transfer  such rights to any other  person or entity,  other
than as provided in this Section 2.10.

     Section 2.11 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,   demands,   instructions  and  other
communications  required  or  permitted  to be given to or made  upon any  party
hereto shall be in writing  delivered to the parties at the  addresses set forth
below (or such other  address as may be provided by one party in a notice to the
other):

     If to Sepracor:

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


                                       -9-
728544.4

<PAGE>




          with a copy to:

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

         If to the Company:

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

         with a copy to:

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

Notice  delivered in accordance  with the foregoing  shall be effective (i) when
delivered, if delivered personally or by facsimile  transmission,  (ii) two days
after being  delivered in the United  States  (properly  addressed  and all fees
paid) for  overnight  delivery  service to a courier  (such as Federal  Express)
which regularly  provides such service and regularly  obtains executed  receipts
evidencing delivery or (iii) five days after being deposited (properly addressed
and stamped for  first-class  delivery) in a daily  serviced  United States mail
box.

     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.

     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 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.


                                      -10-
728544.4

<PAGE>



     Section 3.5 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 3.6 Survival of Agreements,  Representations  and  Warranties.  All
agreements,  representations  and  warranties  made  herein  shall  survive  the
execution and delivery of this Agreement.

     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  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  and judgment  may be entered in any court  having  jurisdiction
thereof.

     Section 3.8  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.



                                      -11-
728544.4

<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 VP Finance and Administration

                               SEPRACOR INC.


                               By:  /s/ Robert Scumaci
                                   -------------------
                               Name:    Robert Scumaci
                               Title:   Senior VP Finance and Administration


                                      -12-
728544.4