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                                                                    Exhibit 10.4

                         REGISTRATION RIGHTS AGREEMENT


         1.  CERTAIN DEFINITIONS.
         As used in this Exhibit E, the following terms shall have the following
respective meanings:

         "COMMISSION" means the Securities and Exchange Commission, or any
other federal agency at the time administering the Securities Act.

         "EXCHANGE ACT" means the Securities Exchange Act of 1934, as
amended, or any successor federal statue, and the rules and regulations of
the Commission issued under such act, as they may, from time to time, be in
effect.

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

         "SECURITIES ACT" means the Securities Act of 1933, as amended, or
any successor federal statute, and the rules and regulations of the
Commission issued under such Act, as they each may, from time to time, be in
effect.

         2.  INCIDENTAL REGISTRATION.

                  (a) Whenever SEPRACOR proposes to file a Registration
Statement covering shares to be sold for the account of SEPRACOR, it will,
prior to such filing, give written notice to UNIVERSITY of its intention to
do so; PROVIDED, that no such notice need be given if no Shares are to be
included therein as a result of a determination of the managing underwriter
pursuant to paragraph 2(b) below. Upon the written request of UNIVERSITY
given within 10 days after SEPRACOR provides such notice, SEPRACOR shall use
its best efforts to cause all Shares which SEPRACOR has been requested by
UNIVERSITY to register to be registered under the Securities Act to the
extent necessary to permit their sale, provided that SPONSOR shall have the
right to postpone or withdraw any registration without obligation to
UNIVERSITY.

                  (b) The right of UNIVERSITY to include its Shares in such
registration pursuant to this Section shall be conditioned upon UNIVERSITY's
participation in the underwriting on the terms set forth herein. UNIVERSITY
shall (together with SEPRACOR, and any officers or directors of SEPRACOR
distributing their securities through such underwriting) enter into an
underwriting agreement in customary form

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with the underwriter or underwriters selected for the underwriting by
SEPRACOR. Notwithstanding any other provision of this Section if the managing
underwriter determines that the inclusion of all shares requested to be
registered would adversely affect the offering, the managing underwriter may
limit the number of Shares to be included in the registration and
underwriting, the securities so included to be apportioned among the holders
of SEPRACOR securities seeking to register their shares, pro rata according
to the number of such securities held by each such holder.

                  (c) Notwithstanding the foregoing, SEPRACOR shall not be
required to include any Shares in a Registration Statement if such Shares can
then be sold pursuant to Rule 144 under the Securities Act.

         3. EXPENSES. SEPRACOR will pay all expenses for all registrations
under this Agreement, except that SEPRACOR shall not be responsible for
underwriting discounts and selling commissions incurred in connection with
the sale of Shares and the fees and expenses of UNIVERSITY's own counsel.

         4. INDEMNIFICATION. In the event any Shares are included in a
registration statement under this Agreement:

                  (a) To the extent permitted by law, SEPRACOR will indemnify
and hold harmless the UNIVERSITY, and each of the UNIVERSITY's officers,
directors, employees and affiliates, any underwriter (as defined in the
Securities Act) for the UNIVERSITY and each Person, if any, who controls the
UNIVERSITY or underwriter within the meaning of the Securities Act or the
Exchange Act against any losses, claims, damages, liabilities, or expenses
(joint or several) to which they may become subject under the Securities Act,
the Exchange Act or other federal or state law, insofar as such losses,
claims, damages or liabilities (or actions in respect thereof) arise out of
or are based upon a Violation (as hereinafter defined), PROVIDED, HOWEVER,
that SEPRACOR will not be required to indemnify any of the foregoing Persons
on account of any losses, claims, damages or liabilities arising from a
Violation if and to the extent that such Violation was made in a preliminary
prospectus and was corrected in a subsequent prospectus that was required by
law to be delivered to the Person making the claim with respect to which
indemnification is sought hereunder (and such subsequent prospectus was made
available by SEPRACOR to permit delivery of such prospectus in a timely
manner), and such subsequent prospectus was not so delivered to such Person;
and SEPRACOR will pay to each such indemnified party, as incurred, any legal
or other expenses reasonably incurred by them in connection with
investigating or defending any such loss, claim, damage, liability, or
action; PROVIDED, HOWEVER, that the indemnity agreement contained in this
Section 4(a) shall not apply to any such loss, claim, damage, liability or
action if settlement thereof is effected without the consent of SEPRACOR
(which consent shall not be unreasonably withheld), nor shall SEPRACOR be
liable in any such case to a particular indemnified party for any such loss,
claim, damage, liability or action to the extent that it arises out of or is
based upon a Violation which occurs in reliance upon and in conformity with
written information furnished expressly for use in connection with such
registration by or on behalf of such indemnified party.

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                  (b) To the extent permitted by law, the UNIVERSITY will
indemnify and hold harmless SEPRACOR, each of its directors, officers, each
of its employees, each Person, if any, who controls SEPRACOR within the
meaning of the Securities Act, any underwriter, against any losses, claims,
damages, liabilities, or expenses (joint or several) to which any of the
foregoing Persons may become subject, under the Securities Act, the Exchange
Act or other federal or state law, insofar as such losses, claims, damages or
liabilities (or actions in respect thereto) arise out of or are based upon
any Violation, in each case to the extent (and only to the extent) that such
Violation occurs in reliance upon and in conformity with written information
furnished by or on behalf of the UNIVERSITY expressly for use in connection
with such registration; and the UNIVERSITY will pay, as incurred, any legal
or other expenses reasonably incurred by any Person intended to be
indemnified pursuant to this Section 4(b), in connection with investigating
or defending any such loss, claim, damage, liability, or action; PROVIDED,
HOWEVER, that the indemnity agreement contained in this Section 4(b) shall
not apply to any such loss, claim, damage, liability or action if settlement
thereof is effected without the consent of the UNIVERSITY, which consent
shall not be unreasonably withheld; and PROVIDED FURTHER, that, in no event
shall the liability of the UNIVERSITY under this Section 4(b) exceed the net
proceeds from the offering received by the UNIVERSITY.

                  (c) Promptly after receipt by an indemnified party under
this Section 4 of notice of the commencement of any action (including any
governmental action), such indemnified party will, if a claim in respect
thereof is to be made against any indemnifying party under this Section 4,
deliver to the indemnifying party a written notice of the commencement
thereof and the indemnifying party shall have the right to participate in,
and, to the extent the indemnifying party so desires, jointly with any other
indemnifying party similarly noticed, to assume the defense thereof with
counsel mutually satisfactory to the parties; PROVIDED, HOWEVER, that an
indemnified party shall have the right to retain its own counsel, with the
fees and expenses to be paid by the indemnifying party, if representation of
such indemnified party by the counsel retained by the indemnifying party
would be inappropriate due to actual or potential differing interests between
such indemnified party and any other party represented by such counsel in
such proceeding. The failure to deliver written notice to the indemnifying
party within a reasonable time of the commencement of any such action shall
not relieve such indemnifying party of any liability to the indemnified party
under this Section 4 except if, and only to the extent that, the indemnifying
party is actually prejudiced thereby; and such failure to deliver written
notice to the indemnifying party will not relieve it of any liability that it
may have to any indemnified party otherwise than under this Section 4.

                  (d) The obligations of SEPRACOR and the UNIVERSITY under
this Section 4 shall survive the completion of any offering of the Shares in
a registration statement under this Agreement and otherwise.

                  (e) The indemnity agreements contained herein shall be in
addition to

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any other rights to indemnification or contribution which any indemnified
party may have pursuant to law or contract and shall remain operative and in
full force and effect regardless of any investigation made or omitted by or
on behalf of any indemnified party.

                  (f) In the event that the indemnity provided in Section
4(a) or 4(b) is by the terms of such Section applicable to a loss, claim,
damage, liability, or expense, but such indemnity is for any reason
unenforceable by the indemnified party, then the party that , under such
Section would have been the indemnifying party (for the purposes of this
subsection, the "indenmifying party") shall contribute to the amount paid or
payable by the indemnified party as a result of such losses, claims, damages,
liabilities or expenses (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 or provides a lesser sum
to the indemnified party than the amount hereinafter calculated, 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 shall be determined by reference to, among other things,
whether the untrue or alleged untrue statement of a material fact or the
omission or alleged omission to state a material fact relates to information
supplied by or on behalf of the indemnifying party or the indemnified party
and the parties' relative intent, knowledge, access to information and
opportunity to correct or prevent such untrue statement or omission. No
Person guilty of fraudulent misrepresentation (within the meaning of section
11(f) of the Securities Act) shall be entitled to contribution from any
Person who was not guilty of such fraudulent misrepresentation.

                  (g) "Violation" means any of the following statements,
omissions or violations: (i) any untrue statement or alleged untrue statement
of a material fact contained in a registration statement under this
Agreement, including any preliminary prospectus or final prospectus contained
therein or any amendments or supplements thereto or any documents filed under
state securities or "blue sky" laws in connection therewith, or (ii) the
omission or alleged omission to state therein a material fact required to be
stated therein, or necessary to make the statements therein not misleading,
or (iii) any violation or alleged violation by SEPRACOR of the Securities
Act, the Exchange Act, any state securities law or any rule or regulation
promulgated under the Securities Act, the Exchange Act or any state
securities law.

         5. REPORTS UNDER THE EXCHANGE ACT. With a view to making available
to the University the benefits of Rule 144 under the Securities Act and any
other rule or regulation of the Commission that may at any time permit the
University to sell securities of SEPRACOR to the public without registration
or pursuant to a registration

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on Form S-3, SEPRACOR agrees to:

                  (a) make and keep public information available, as those
terms are understood and defined in Rule 144 under the Securities Act, at all
times after the effective date of the first registration statement filed by
SEPRACOR for the offering of its securities to the general public;

                  (b) file with the Commission in a timely manner all reports
and other documents required of SEPRACOR under the Securities Act and the
Exchange Act; and

                  (d) furnish to the UNIVERSITY, so long as the UNIVERSITY
owns any Shares, forthwith upon request (i) a written statement by SEPRACOR
that it has complied with the reporting requirements of Rule 144 under the
Securities Act, the Securities Act and the Exchange Act, and (ii) a copy of
the most recent annual or quarterly report of SEPRACOR and such other reports
and documents so filed by SEPRACOR which are made public.

         6.  MISCELLANEOUS.

                  (a) UNIVERSITY shall treat as confidential any notice from
SEPRACOR regarding plans to file a Registration Statement and shall not
disclose such information to any person other than as necessary to exercise
its rights hereunder.

                  (b) SEPRACOR shall not be required to include any Shares in
a Registration Statement unless UNIVERSITY furnishes to SEPRACOR in writing
such information regarding UNIVERSITY as SEPRACOR may reasonably request in
writing in connection with the Registration Statement or as shall be required
in connection therewith by the Commission or any state securities law
authorities.


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