<PAGE>
                                                                   Exhibit 10.19

                                                                  EXECUTION COPY

                            IMARX THERAPEUTICS, INC.
                          REGISTRATION RIGHTS AGREEMENT

            THIS REGISTRATION RIGHTS AGREEMENT (this "Agreement") is made as of
January 19, 2001 by and among ImaRx Therapeutics, Inc., a Delaware corporation
(the "Company"), ELAN INTERNATIONAL SERVICES, LTD., a Bermuda exempted limited
liability company ("EIS"), and ELAN PHARMA INTERNATIONAL LIMITED, an Irish
private limited liability company ("EPIL").

                                R E C I T A L S:

            A. Pursuant to a Securities Purchase Agreement dated as of the date
hereof by and among the Company, EIS and EPIL (the "Purchase Agreement"), (i)
EIS has acquired, or will acquire in the future, (a) certain shares of Series B
Preferred Stock of the Company (the "Series B Preferred Stock") convertible into
shares of common stock of the Company (the "Common Stock") or Series C Preferred
Stock of the Company (the "Series C Preferred Stock"), as the case may be, and
(b) certain shares of Series C Preferred Stock of the Company convertible into
shares of Common Stock, and (ii) EPIL has acquired a certain note of the Company
(the "Note") convertible into shares of Common Stock or Series C Preferred
Stock, as the case may be. The Series B Preferred Stock, the Series C Preferred
Stock and the Note collectively are referred to herein as the "Securities".

            B. The execution of the Purchase Agreement has occurred on the date
hereof and it is a condition to the closing of the transactions contemplated
thereby that the parties execute and deliver this Agreement.

            C. The parties desire to set forth herein their agreement on the
terms and subject to the conditions set forth herein related to the granting of
certain registration rights to the Holders (as defined below) relating to the
Common Stock, if any, held and the Common Stock issuable upon conversion or
exercise of the Securities by such Holders.

                               A G R E E M E N T:

            The parties hereto agree as follows:

      1.    Certain Definitions.  As used in this Agreement, the following
terms shall have the following respective meanings:

            "Commission" shall mean the U.S. Securities and Exchange Commission.
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                                      -2-


            "Exchange Act" shall mean the U.S. Securities Exchange Act of 1934,
as amended, and the rules and regulations of the Commission thereunder, all as
the same shall be in effect from time to time.

            "Holders" or "Holders of Registrable Securities" shall mean EIS,
EPIL and any Person who shall have acquired Registrable Securities from EIS or
EPIL as permitted herein and in the Purchase Agreement, either individually or
jointly, as the case may be, in a transaction pursuant to which registration
rights are transferred pursuant to Section 10 hereof.

            "Initial Offering" shall mean the Company's first firm commitment
underwritten public offering of its Common Stock registered under the Securities
Act.

            "Person" shall mean an individual, a partnership, a company, an
association, a joint stock company, a trust, a joint venture, an unincorporated
organization or a governmental or quasi-governmental entity, or any department,
agency or political subdivision thereof.

            "Registrable Securities" means (i) any shares of Common Stock issued
or issuable upon conversion or exercise of the Securities; and (ii) any shares
of Common Stock issued or issuable in respect of the securities referred to in
clause (i) above, until, in the case of any such security, it is effectively
registered under the Securities Act and disposed of in accordance with the
registration statement covering it; excluding in all cases, however, any
Registrable Securities that are sold by a Person to the public either pursuant
to a registration statement or under Rule 144 promulgated under the Securities
Act, as such rule may be amended from time to time, or any similar rule or
regulation hereafter adopted by the Commission, and Registrable Securities sold
by a Person in a transaction (including a transaction pursuant to a registration
statement under this Agreement and a transaction pursuant to Rule 144
promulgated under the Securities Act) in which registration rights are not
transferred pursuant to Section 10 hereof. Whenever a number or percentage of
Registrable Securities is to be determined pursuant to this Agreement, each then
outstanding Security that is convertible into or exercisable for shares of
Common Stock will be deemed to be equal to the number of shares of Common Stock
for which such Security is then so convertible or exercisable.

            The terms "register," "registered" and "registration" refer to a
registration effected by preparing and filing a registration statement in
compliance with the Securities Act.

            "Registration Expenses" shall mean all expenses, other than Selling
Expenses, incurred by the Company in complying with Sections 2 or 3 hereof,
including without limitation, all registration, filing fees, exchange listing
fees (if shares of Common Stock are then listed on a securities exchange),
printing expenses, escrow fees, fees and disbursements of counsel for the
Company, blue sky fees and expenses, the expense of any special audits incident
to or required by any such registration.
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                                      -3-


            "Securities Act" shall mean the Securities Act of 1933, as amended.

            "Selling Expenses" shall mean all underwriting discounts, selling
commissions and stock transfer taxes and the reasonable costs, fees and expenses
of any accountants, attorneys or other experts retained by the Holders.

      2.    Demand Registrations.

            (a) Requests for Registration. From and after the Initial Offering,
any Holder or Holders who collectively hold Registrable Securities representing
at least 5% of the Registrable Securities then outstanding shall have the right
(subject to the limitations below) to request registration under the Securities
Act of all or part of their Registrable Securities on Form S-1 or S-3 (or any
successor form to Form S-1 or S-3, or any similar short-form registration
statement) (a "Demand Registration"). The request for the Demand Registration
shall specify the approximate number of Registrable Securities requested to be
registered, which must have a minimum expected aggregate offering price to the
public of at least, (x) within the first 12 months following the consummation of
an Initial Offering, U.S.$5,000,000, net of underwriting discounts and
commissions, and (y) thereafter, U.S.$2,000,000. Within 10 days after receipt of
any such request, the Company will give written notice of such requested
registration to all other Holders of Registrable Securities. The Company shall
include such other Holders' Registrable Securities in such offering if they have
responded affirmatively within 10 days after the receipt of the Company's
notice. The Holders shall be permitted only one Demand Registration hereunder. A
registration will not count as a permitted Demand Registration until it has
become effective (unless such Demand Registration has not become effective due
solely to the fault of the Holders requesting such registration or a request by
such Holders that such registration be withdrawn).

            (b) Priority on Demand Registrations. If a Demand Registration is an
underwritten offering and the managing underwriters advise the Company in
writing that in their opinion the number of Registrable Securities and, if
permitted hereunder, other securities requested to be included in such offering,
exceeds the number of Registrable Securities and other securities, if any, which
can be sold in such offering without adversely affecting the marketability of
the offering, the Company will include in such registration:

            (i) first, the Registrable Securities requested to be included in
      such registration by the Holders (or, if necessary, such Registrable
      Securities pro rata among the Holders thereof based upon the number of
      Registrable Securities owned by each such Holder); and

            (ii) thereafter, other securities requested to be included in such
      registration, as determined by the Company.
<PAGE>
                                      -4-


            (c) Restrictions on Demand Registration. The Company may postpone or
suspend for up to three months in any 12-month period the filing or the
effectiveness of a registration statement for a Demand Registration if the
Company determines in good faith that such Demand Registration (i) would
reasonably be expected to have a material adverse effect on (x) any proposal or
plan by the Company to engage in any financing, acquisition or disposition of
assets (other than in the ordinary course of business) or (y) any merger,
consolidation, tender offer or similar transaction or (ii) would require
disclosure of any information that the board of directors of the Company
determines in good faith the disclosure of which would be detrimental to the
Company; provided, however, that in such event, the Holders initially requesting
such Demand Registration will be entitled to withdraw such request and, if such
request is withdrawn, such Demand Registration will not count as a permitted
Demand Registration hereunder and the Company will pay any Registration Expenses
in connection with such registration.

            (d) Selection of Underwriters. The Holders will have the right to
select the investment banker(s) and manager(s) to administer an offering
pursuant to the Demand Registration, subject to the Company's prior written
approval, which will not be unreasonably withheld, delayed or conditioned.

            (e) Other Registration Rights. Except as provided in this Agreement,
so long as any Holder owns any Registrable Securities, the Company will not
grant to any Persons the right to require the Company to register any equity
securities of the Company, or any securities convertible or exchangeable into or
exercisable for such securities, which conflicts with the rights granted to the
Holders hereunder, without the prior written consent of the Holders of at least
50% of the Registrable Securities.

      3.    Piggyback Registrations.

            (a) Right to Piggyback. If at any time the Company shall propose to
register shares of Common Stock under the Securities Act (other than in a
registration statement on Form S-3 relating to sales of securities to
participants in a Company dividend reinvestment plan, or Form S-4 or S-8 or any
successor form or in connection with an acquisition or exchange offer or an
offering of securities solely to the existing shareholders or employees of the
Company or a registration statement on Form S-1 relating to the Initial
Offering) (each, a "Piggyback Registration"), the Company (i) will give prompt
written notice to all Holders of Registrable Securities of its intention to
effect such a registration at least 30 days prior to the filing of such
registration statement and (ii) subject to Section 3(b) and the other terms of
this Agreement, will include in such registration all Registrable Securities
which are permitted under applicable securities laws to be included in the form
of registration statement selected by the Company and with respect to which the
Company has received written requests for inclusion therein within 30 days after
the receipt of the Company's notice. The Holders will be permitted to withdraw
all or any part of the Registrable Securities from a Piggyback Registration at
any time prior to the effective date of such Piggyback Registration.
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                                      -5-


            (b) Priority on Piggyback Registrations. If a Piggyback Registration
is to be an underwritten offering, and the managing underwriters advise the
Company in writing that in their opinion the number of securities requested to
be included in such registration exceeds the number which can be sold in such
offering without adversely affecting the marketability of the offering, the
Company will include in such registration:

            (i)   first, the securities the Company proposes to sell;

            (ii) second, the Registrable Securities requested to be included in
      such registration by the Holders and any securities requested to be
      included in such registration by any other Person other than Persons
      having a lower priority of registration than the Holders, pro rata among
      the Holders of such Registrable Securities and such other Persons, on the
      basis of the number of securities requested to be included in such
      registration by each of such Holders and such other Persons; and

            (iii) thereafter, other securities requested to be included in such
      registration, as determined by the Company.

            No such reduction shall reduce the securities being offered by the
Company for its own account to be included in such registration statement. The
Holders of any Registrable Securities included in such an underwritten offering
will execute an underwriting agreement in customary form and in form and
substance satisfactory to the managing underwriters.

            (c) Right to Terminate Registration. If at any time after giving
written notice of its intention to register any of its securities as set forth
in Section 3(a) and prior to the effective date of the registration statement
filed in connection with such registration, the Company shall determine for any
reason not to register such securities, the Company may, at its election, give
written notice of such determination to each Holder of Registrable Securities
and thereupon be relieved of its obligation to register any Registrable
Securities in connection with such registration (but not from its obligation to
pay the Registration Expenses in connection therewith as provided herein).

            (d) Selection of Underwriters. The Company will have the right to
select the investment banker(s) and manager(s) to administer an offering
pursuant to a Piggyback Registration.

      4.    Expenses of Registration.

            Except as otherwise provided herein or as may otherwise be
prohibited by applicable law, all Registration Expenses incurred in connection
with all registrations pursuant to Sections 2 and 3 hereof shall be borne by the
Company. All Selling Expenses relating to securities registered on behalf of the
Holders of Registrable Securities shall be borne by such Holders.
<PAGE>
                                      -6-


      5. Holdback Agreements. Each Holder agrees, if requested by the managing
underwriters in an underwritten offering of Common Stock or securities
convertible for Common Stock of the Company (including without limitation the
Company's Initial Offering of Common Stock), not to exercise their rights
pursuant to Section 2 hereof or to effect any offer, sale, distribution or
transfer, including a sale pursuant to Rule 144 (or any similar provision then
effect) under the Securities Act (except as part of such underwritten
registration), during the 10-day period prior to, and during the 180-day period
in the case of the Company's Initial Offering or a 90-day period in the case of
any other offering of Common Stock (or, in each case, such shorter period as may
be agreed to in writing by the Company and the Holders of at least 50% of the
Registrable Securities) following, the effective date of such Registration
Statement; provided, however, that no Holder shall be required to enter into
more than one such agreement in any 12-month period.

      6.    Registration Procedures.

            Whenever the Holders of Registrable Securities have requested that
any Registrable Securities be registered pursuant to this Agreement, the Company
will use all reasonable efforts to effect the registration and the sale of such
Registrable Securities in accordance with the intended method or methods of
distribution thereof, and pursuant thereto the Company will as expeditiously as
possible:

            (a) subject to Section 2(c) hereof, prepare and file with the
      Commission a registration statement on any appropriate form for which the
      Company qualifies with respect to such Registrable Securities and use all
      reasonable efforts to cause such registration statement to become
      effective (provided that before filing a registration statement or
      prospectus or any amendments or supplements thereto, the Company will (i)
      furnish to the counsel selected by the Holders copies of all such
      documents proposed to be filed, which documents will be subject to the
      reasonable review of such counsel, and (ii) notify each Holder of
      Registrable Securities covered by such registration of any stop order
      issued or threatened by the Commission);

            (b) subject to Section 2(c) hereof, prepare and file with the
      Commission such amendments and supplements to such registration statement
      and the prospectus used in connection therewith as may be reasonably
      necessary to keep such registration statement effective for a period equal
      to the shorter of (i) six months and (ii) the time by which all securities
      covered by such registration statement have been sold, and comply with the
      provisions of the Securities Act with respect to the disposition of all
      securities covered by such registration statement during such period in
      accordance with the intended methods of disposition by the sellers thereof
      set forth in such registration statement;

            (c) furnish to each seller of Registrable Securities such number of
      copies of such registration statement, each amendment and supplement
      thereto, the prospectus included in such registration statement (including
      each preliminary prospectus) and such
<PAGE>
                                      -7-


other documents as such seller may reasonably request in order to facilitate the
disposition of the Registrable Securities owned by such seller;

            (d) use its reasonable efforts to register or qualify such
      Registrable Securities under the securities or blue sky laws of such
      jurisdictions as any seller of Registrable Securities reasonably requests
      and do any and all other acts and things which may be reasonably necessary
      or advisable to enable such seller to consummate the disposition in such
      jurisdictions of the Registrable Securities owned by such seller (provided
      that the Company will not be required to (i) qualify generally to do
      business in any jurisdiction where it would not otherwise be required to
      qualify but for this Section 6(d), (ii) subject itself to taxation in any
      jurisdiction or (iii) take any action that would subject it to general
      service of process in any such jurisdiction);

            (e) notify each seller of such Registrable Securities, at any time
      when a prospectus relating thereto is required to be delivered under the
      Securities Act, of the happening of any event as a result of which the
      prospectus included in such registration statement contains an untrue
      statement of a material fact or omits any fact necessary to make the
      statements therein not misleading, and, at the request of any such seller,
      the Company will prepare a supplement or amendment to such prospectus so
      that, as thereafter delivered to the purchasers of such Registrable
      Securities, such prospectus will not contain an untrue statement of a
      material fact or omit to state any fact necessary to make the statements
      therein not misleading; provided, however, that the Company shall not be
      required to amend the registration statement or supplement the Prospectus
      for a period of up to six months if the board of directors determines in
      good faith that to do so would reasonably be expected to have a material
      adverse effect on any proposal or plan by the Company to engage in any
      financing, acquisition or disposition of assets (other than in the
      ordinary course of business) or any merger, consolidation, tender offer or
      similar transaction or would require the disclosure of any information
      that the board of directors determines in good faith the disclosure of
      which would be detrimental to the Company, it being understood that the
      period for which the Company is obligated to keep the Registration
      Statement effective shall be extended for a number of days equal to the
      number of days the Company delays amendments or supplements pursuant to
      this provision. Upon receipt of any notice pursuant to this Section 6(e),
      the Holders shall suspend all offers and sales of securities of the
      Company and all use of any prospectus until advised by the Company that
      offers and sales may resume, and shall keep confidential the fact and
      content of any notice given by the Company pursuant to this Section 6(e);

            (f) cause all such Registrable Securities to be listed on each
      securities exchange, if any, on which similar securities issued by the
      Company are then listed;

            (g) provide a transfer agent and registrar for all such Registrable
      Securities not later than the effective date of such registration
      statement;
<PAGE>
                                      -8-


            (h) enter into such customary agreements (including underwriting
      agreements in customary form) and take all such other actions as the
      Holders of a majority of the Registrable Securities being sold or the
      underwriters, if any, reasonably request in order to expedite or
      facilitate the disposition of such Registrable Securities;

            (i) make reasonably available for inspection by a representative of
      the Holders of Registrable Securities included in the registration
      statement, any underwriter participating in any disposition pursuant to
      such registration statement and any attorney, accountant or other agent
      retained by any such seller or underwriter, all pertinent financial and
      other records, pertinent corporate documents and properties of the
      Company, and cause the Company's officers, directors, employees and
      independent accountants to supply all information reasonably requested by
      any such seller, underwriter, attorney, accountant or agent in connection
      with such registration statement;

            (j) otherwise use its reasonable efforts to comply with all
      applicable rules and regulations of the Commission, and make available to
      its security holders, as soon as reasonably practicable, an earnings
      statement covering the period of at least 12 months beginning with the
      first day of the Company's first full calendar quarter after the effective
      date of the registration statement, which earnings statement shall satisfy
      the provisions of Section 11(a) of the Securities Act and Rule 158
      thereunder;

            (k) in the event of the issuance of any stop order suspending the
      effectiveness of a registration statement, or of any order suspending or
      preventing the use of any related prospectus or suspending the
      qualification of any shares of Common Stock included in such registration
      statement for sale in any jurisdiction, use all reasonable efforts
      promptly to obtain the withdrawal of such order; and

            (l) if the registration is an underwritten offering, use all
      reasonable efforts to obtain a so-called "cold comfort" letter from the
      Company's independent public accountants in customary form and covering
      such matters of the type customarily covered by cold comfort letters.

      7.    Obligations of Holders.

            Whenever the Holders of Registrable Securities sell any Registrable
Securities pursuant to a Demand Registration or a Piggyback Registration, such
Holders shall be obligated to comply with the applicable provisions of the
Securities Act, including the prospectus delivery requirements thereunder, and
any applicable state securities or blue sky laws. In addition, each Holder of
Registrable Securities will be deemed to have agreed by virtue of its
acquisition of such Registrable Securities that, upon receipt of any notice
described in Section 6(e), such holder will forthwith discontinue disposition of
such Registrable Securities covered by such registration statement or prospectus
until such holder's receipt of the copies of the supplemented or amended
<PAGE>
                                      -9-


prospectus contemplated by Section 6(e), or until it is advised in writing by
the Company that the use of the applicable prospectus may be resumed, and has
received copies of any additional or supplemental filings that are incorporated
or deemed to be incorporated by reference in such prospectus.

      8.    Indemnification.

            (a) The Company agrees to indemnify, to the fullest extent permitted
by applicable law, each Holder of Registrable Securities, its officers and
directors and each Person who controls such Holder (within the meaning of the
Securities Act) against all losses, claims, damages, liabilities, expenses or
any amounts paid in settlement of any litigation, investigation or proceeding
commenced or threatened (collectively, "Claims") to which each such indemnified
party may become subject under the Securities Act insofar as such Claim arose
out of (i) any untrue or alleged untrue statement of material fact contained, on
the effective date thereof, in any registration statement, prospectus or
preliminary prospectus or any amendment thereof or supplement thereto or (ii)
any omission or alleged omission to state therein a material fact required to be
stated therein or necessary to make the statements therein not misleading,
except insofar as such Claims are caused by or contained in any information
furnished in writing to the Company by such Holder or a partner, officer,
director or controlling person of such Holder, expressly for use therein, by
such Holder's failure to deliver a copy of the registration statement or
prospectus or any amendments or supplements thereto after the Company has
furnished such Holder with a sufficient number of copies of the same or by such
Holder's failure to comply with applicable securities laws. In connection with
an underwritten offering, the Company will indemnify the underwriters, their
officers and directors and each Person who controls the underwriters (within the
meaning of the Securities Act) to the same extent as provided above with respect
to the indemnification of the Holders of Registrable Securities.

            (b) In connection with any registration statements in which a Holder
of Registrable Securities is participating, each such Holder will, to the
fullest extent permitted by applicable law, indemnify the Company, its directors
and officers and each Person who controls the Company (within the meaning of the
Securities Act) against any and all Claims to which each such indemnified party
may become subject under the Securities Act insofar as such Claim arose out of
(i) any untrue or alleged untrue statement of material fact contained, on the
effective date thereof, in any registration statement, prospectus or preliminary
prospectus or any amendment thereof or supplement thereto, (ii) any omission or
alleged omission to state therein a material fact required to be stated therein
or necessary to make the statements therein not misleading or (iii) any failure
to comply with applicable securities laws; provided that with respect to a Claim
arising pursuant to clause (i) or (ii) above, the material misstatement or
omission is contained in the information such Holder provided to the Company
pursuant to Section 11 hereof; provided, further, that the obligation to
indemnify will be individual to each Holder and will be limited to
<PAGE>
                                      -10-


the amount of proceeds received by such Holder from the sale of Registrable
Securities pursuant to such registration statement.

            (c) Any Person entitled to indemnification hereunder will (i) give
prompt written notice to the indemnifying party of any claim with respect to
which it seeks indemnification (but the failure to provide such notice shall not
release the indemnifying party of its obligation under paragraphs (a) and (b),
unless and then only to the extent that, the indemnifying party has been
prejudiced by such failure to provide such notice) and (ii) unless in such
indemnified party's reasonable judgment, based on written advice of counsel, a
conflict of interest between such indemnified and indemnifying parties may exist
with respect to such claim, permit such indemnifying party to assume the defense
of such claim with counsel reasonably satisfactory to the indemnified party. An
indemnifying party who is not entitled to, or elects not to, assume the defense
of a claim will not be obligated to pay the fees and expenses of more than one
counsel for all parties indemnified by such indemnifying party with respect to
such claim, unless in the reasonable judgment of any indemnified party, based on
written advice of counsel, a conflict of interest may exist between such
indemnified party and any other of such indemnified parties with respect to such
claim.

            (d) The indemnifying party shall not be liable to indemnify an
indemnified party for any settlement, or consent to judgment of any such action
effected without the indemnifying party's written consent (but such consent will
not be unreasonably withheld, delayed or conditioned). Furthermore, the
indemnifying party shall not, except with the prior written approval 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 each indemnified party of a release from all liability
in respect of such claim or litigation without any payment or consideration
provided by each such indemnified party.

            (e) If the indemnification provided for in this Section 8 is
unavailable to an indemnified party under clauses (a) and (b) above in respect
of any losses, claims, damages or liabilities referred to therein, then each
indemnifying party, in lieu of indemnifying such indemnified party, shall
contribute to the amount paid or payable by such indemnified party as a result
of such losses, claims, damages or liabilities in such proportion as is
appropriate to reflect not only the relative benefits received by the Company,
the underwriters, the sellers of Registrable Securities and any other sellers
participating in the registration statement from the sale of shares pursuant to
the registered offering of securities for which indemnity is sought but also the
relative fault of the Company, the underwriters, the sellers of Registrable
Securities and any other sellers participating in the registration statement in
connection with the misstatement or omission which resulted in such losses,
claims, damages or liabilities, as well as any other relevant equitable
considerations. The relative benefits received by the Company, the underwriters,
the sellers of Registrable Securities and any other sellers participating in the
registration statement shall be deemed to be based on the relative relationship
of the total net proceeds from the offering (before deducting
<PAGE>
                                      -11-


expenses) to the Company, the total underwriting commissions and fees from the
offering (before deducting expenses) to the underwriters and the total net
proceeds from the offering (before deducting expenses) to the sellers of
Registrable Securities and any other sellers participating in the registration
statement. The relative fault of the Company, the underwriters, the sellers of
Registrable Securities and any other sellers participating in the registration
statement 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 the Company
or by the sellers of Registrable Securities and the parties' relative intent,
knowledge, access to information and opportunity to correct or prevent such
statement or omission; provided that in no event shall the liability of any
selling Holder hereunder be greater in amount than the dollar amount of the
proceeds received by such Holder upon the sale of the Registrable Securities
giving rise to such indemnification obligation.

            (f) The indemnification provided for under this Agreement will
remain in full force and effect regardless of any investigation made by or on
behalf of the indemnified party or any officer, director or controlling person
of such indemnified party and will survive the transfer of the Registrable
Securities.

      9.    Participation in Underwritten Registrations.

            No Holder may participate in any registration hereunder which is
underwritten unless such Holder (a) agrees to sell such Holder's securities on
the basis provided in any underwriting arrangements approved by the Holder or
Holders entitled hereunder to approve such arrangements, (b) as expeditiously as
possible notifies the Company of the occurrence of any event as a result of
which any prospectus contains an untrue statement of material fact or omits to
state a material fact required to be stated therein or necessary to make the
statements therein not misleading and (c) completes and executes all
questionnaires, powers of attorney, indemnities, underwriting agreements and
other documents reasonably required under the terms of such underwriting
arrangements.

      10.   Transfer of Registration Rights.

            The rights granted to any Holder under this Agreement may be
assigned to any permitted transferee of Registrable Securities, in connection
with any transfer or assignment of Registrable Securities by a Holder; provided,
however, that: (a) such transfer is otherwise effected in accordance with
applicable securities laws, (b) such transfer is permitted by the Purchase
Agreement, (c) if not already a party hereto, the assignee or transferee agrees
in writing prior to such transfer to be bound by the provisions of this
Agreement applicable to the transferor and (d) EIS shall act as agent and
representative for such Holder for the giving and receiving of notices
hereunder.
<PAGE>
                                      -12-


      11.   Information by Holder.

            Each Holder shall furnish to the Company such written information
regarding such Holder and any distribution proposed by such Holder as the
Company may reasonably request in writing and as shall be reasonably required in
connection with any registration, qualification or compliance referred to in
this Agreement and shall promptly notify the Company of any changes in such
information.

      12.   Exchange Act Compliance.

            The Company shall comply with all of the reporting requirements of
the Exchange Act then applicable to it, if any, and shall comply with all other
public information reporting requirements of the Commission that are conditions
to the availability of Rule 144 for the sale of the Registrable Securities. The
Company shall cooperate with each Holder in supplying such information as may be
necessary for such Holder to complete and file any information reporting forms
presently or hereafter required by the Commission as a condition to the
availability of Rule 144.

      13.   Termination of Registration Rights.

            All registration rights and obligations (including, without
limitation, under Section 5) under this Agreement shall terminate and be of no
further force and effect, as to any particular Holder, at such time as all
Registrable Securities held by such Holder are eligible to be sold without
compliance with the registration requirements of the Securities Act pursuant to
Rule 144(k) promulgated thereunder or have been resold pursuant to a
registration statement hereunder.

      14.   Miscellaneous.

            (a) No Inconsistent Agreements. The Company will not hereafter enter
into any agreement with respect to its securities that is inconsistent with or
violates the rights granted to the Holders of Registrable Securities in this
Agreement without the prior written consent of a majority in interest of such
Registrable Securities.

            (b) Remedies. Any Person having rights under any provision of this
Agreement will be entitled to enforce such rights specifically to recover
damages caused by reason of any breach of any provision of this Agreement and to
exercise all other rights granted by law. The parties hereto agree and
acknowledge that money damages may not be an adequate remedy for any breach of
the provisions of this Agreement and that any party may in its sole discretion
apply to any court of law or equity of competent jurisdiction (without posting
any bond or other security) for specific performance and for other injunctive
relief in order to enforce or prevent
<PAGE>
                                      -13-


violation of the provisions of this Agreement; provided, however, that in no
event shall any Holder have the right to enjoin, delay or interfere with any
offering of securities by the Company.

            (c) Amendments and Waivers. Except as otherwise provided herein, the
provisions of this Agreement may be amended or waived only with the prior
written consent of the Company and Holders of at least 50% of the Registrable
Securities; provided, however, that without the prior written consent of all the
Holders, no such amendment or waiver shall reduce the foregoing percentage
required to amend or waive any provision of this Agreement.

            (d) Successors and Assigns. This Agreement and all of the provisions
hereof shall be binding upon and inure to the benefit of the parties and their
respective successors and permitted assigns. This Agreement may be transferred
along with such Holder's Registrable Securities by EIS, EPIL and their permitted
assigns and transferees to their respective affiliates and subsidiaries, as well
as any special purpose financing or similar vehicle established by EIS or EPIL.
Other than as set forth above, no party shall transfer or assign this Agreement
without the prior written consent of the other party, which will not be
unreasonably withheld, delayed or conditioned. In addition, whether or not any
express assignment has been made, the provisions of this Agreement which are for
the benefit of Holders of Registrable Securities are also for the benefit of,
and enforceable by, any permitted transferee of Registrable Securities, in
accordance with Section 10 hereof.

            (e) Severability. In case any provision of this Agreement shall be
invalid, illegal or unenforceable, the validity, legality and enforceability of
the remaining provisions shall not be in any way affected or impaired thereby.

            (f) Counterparts and Facsimile. This Agreement may be executed in
any number of counterparts, and each such counterpart hereof shall be deemed to
be an original instrument, but all such counterparts together shall constitute
one agreement. This Agreement may be signed and delivered to the other party by
facsimile transmission; such transmission shall be deemed a valid signature.

            (g)   Descriptive Headings.  The section and paragraph headings
contained in this Agreement are for reference purposes only and shall not
affect in any way the meaning or interpretation of this Agreement.

            (h) Governing Law; Disputes. This Agreement shall be governed by and
construed in accordance with the internal laws of the State of New York, without
giving effect to principles of conflicts of laws. Any dispute under this
Agreement that is not settled by mutual consent shall be finally adjudicated by
any federal or state court sitting in the City, County and State of New York,
and each party consents to the exclusive jurisdiction of such courts (or any
appellate court therefrom) over any such dispute.
<PAGE>
                                      -14-


            (i) Notices. All notices, demands and requests of any kind to be
delivered to any party in connection with this Agreement shall be in writing and
shall be deemed to have been duly given if personally or hand delivered or if
sent by internationally-recognized overnight courier or by registered or
certified mail, return receipt requested and postage prepaid, or by facsimile
transmission, addressed as follows:

            (i)     if to the Company, to:

                    ImaRx Therapeutics, Inc.
                    1635 East 18th Street
                    Tucson, AZ  85719
                    Attention:  Chief Financial Officer
                    Facsimile:  (520) 791-2437

                    with a copy to:

                    Fennemore Craig
                    3003 North Central Avenue

                    Suite 2600
                    Phoenix, AZ 85012
                    Attention:  Sarah A. Strunk, Esq.
                    Facsimile:  (602) 916-5527

            (ii)(a) if to EIS, to:

                    Elan International Services, Ltd.
                    102 St. James Court
                    Flatts, Smiths Parish

                    Bermuda FL 04
                    Attention:  Chief Executive Officer
                    Facsimile:  (441) 292-2224

                (b) if to EPIL, to:

                    Elan Pharma International Limited
                    Will House
                    Shannon Business Park
                    Shannon, Co. Clare
                    Ireland
                    Attention:  Secretary
                    Facsimile:  011-353-61-362097
<PAGE>
                                      -15-


            with a copy, in the case of (a) or (b) above, to:

                  Cahill Gordon & Reindel
                  80 Pine Street
                  New York, New York  10005
                  Attention:  William M. Hartnett, Esq.
                  Facsimile:  (212) 269-5420

or to such other address as the party to whom notice is to be given may have
furnished to the other party hereto in writing in accordance with provisions of
this Section 14(i). Any such notice or communication shall be deemed to have
been effectively given (i) in the case of personal or hand delivery, on the date
of such delivery, (ii) in the case of an internationally-recognized overnight
delivery courier, on the second business day after the date when sent, (iii) in
the case of mailing, on the fifth business day following that day on which the
piece of mail containing such communication is posted and (iv) in the case of
facsimile transmission, on the date of telephone confirmation of receipt.

            (j) Entire Agreement. This Agreement constitutes the full and entire
understanding and agreement of the parties with regard to the subject matter
hereof and supersedes all prior agreements and understandings among the parties
with respect thereto.

                            [Signature page follows]
<PAGE>
            IN WITNESS WHEREOF, the parties have executed this Registration
Rights Agreement as of the date first written above.

                                 IMARX THERAPEUTICS, INC.


                                 By:  \s\ R. Michael Rodgers
                                     _________________________
                                     Name:  R. Michael Rodgers
                                      Title:  Vice President and Secretary


                                  ELAN INTERNATIONAL SERVICES, LTD.


                                  By:  \s\ Kevin Insley
                                       _________________________
                                       Name:  Kevin Insley
                                       Title:  President and Chief Financial
                                       Officer

                                  ELAN PHARMA INTERNATIONAL LIMITED


                                  By:  \s\ Kevin Insley
                                       _________________________
                                       Name:  Kevin Insley
                                       Title:  Authorized Signatory