EXHIBIT 10.19
















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                          REGISTRATION RIGHTS AGREEMENT

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                                October 20, 1997



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                                TABLE OF CONTENTS

                                                                                

         1.       Registration Rights...........................................
                  1.1      Definitions..........................................
                  1.2      Shelf Registration...................................
                  1.3      Company Registration.................................
                  1.4      Obligations of the Company...........................
                  1.5      Furnish Information..................................
                  1.6      Expenses of Registration.............................
                  1.7      Expenses of Company Registration.....................
                  1.8      Underwriting Requirements............................
                  1.9      Delay of Registration................................
                  1.10     Indemnification......................................
                  1.11     Reports Under Securities Exchange Act of 1934........
                  1.12     Assignment of Registration Rights....................
                  1.13     Limitations on Subsequent Registration Rights........
                  1.14     "Market Stand-Off" Agreement.........................
                  1.15     No Required Sale.....................................

         2.       Miscellaneous.................................................
                  2.1      Successors and Assigns...............................
                  2.2      Governing Law........................................
                  2.3      Counterparts.........................................
                  2.4      Titles and Subtitles.................................
                  2.5      Notices..............................................
                  2.6      Expenses.............................................
                  2.7      Amendments and Waivers...............................
                  2.8      Severability.........................................
                  2.9      Nominees for Beneficial Owners.......................
                  2.10     Specific Performance.................................
                  2.11     No Inconsistent Agreements...........................
                  2.12     Entire Agreement.....................................




<PAGE>
                          REGISTRATION RIGHTS AGREEMENT


                  THIS REGISTRATION  RIGHTS AGREEMENT is made as of the 20th day
of October,  1997 by and  between  Exogen,  Inc.,  a Delaware  corporation  (the
"Company"),  and the investors  listed on Schedule 1 hereto  (collectively,  the
"Investors").

                                    RECITALS

                  WHEREAS,  the  Company  and the  Investors  are parties to the
Common Stock  Purchase  Agreement  of even date  herewith  (the "Stock  Purchase
Agreement");

                  WHEREAS,  in order to induce  the  Company  to enter  into the
Stock  Purchase  Agreement  and to induce the  Investors  to invest funds in the
Company pursuant to the Stock Purchase Agreement,  the Investors and the Company
hereby agree that this  Agreement  shall  govern the rights of the  Investors to
cause the Company to register  shares of Common Stock  issuable to the Investors
and certain other matters as set forth herein;

                  NOW, THEREFORE, THE PARTIES HEREBY AGREE AS FOLLOWS:

                  1.       Registration Rights. The Company covenants and agrees
                           as follows:

                           1.1      Definitions. For purposes of this Section 1:

                                    (a) The term "Act" means the  Securities Act
of 1933, as amended.

                                    (b) The terms  "Form  S-3"  means  such form
under the Act as in effect on the date hereof or any registration form under the
Act subsequently  adopted by the SEC which permits inclusion or incorporation of
substantial  information  by reference to other  documents  filed by the Company
with the SEC.

                                    (c) The term "register,"  "registered,"  and
"registration"  refer to a  registration  effected  by  preparing  and  filing a
registration statement or similar document in compliance with the Securities Act
of  1933,  as  amended  (the  "Act"),   and  the   declaration  or  ordering  of
effectiveness of such registration statement or document;

                                    (d) The term "Registrable  Securities" means
(1) the Common Stock issued pursuant to the Stock Purchase Agreement and (2) any
Common  Stock of the  Company  issued as (or  issuable  upon the  conversion  or
exercise of any warrant,  right or other security which is issued as) a dividend
or other  distribution with respect to, or in exchange for or in replacement of,
such Common Stock,  excluding in all cases, however, any Registrable  Securities
which are sold, assigned,  pledged,  hypothecated or otherwise disposed of by an
Investor in a transaction in which such  Investor's  rights under this Agreement
are not assigned or assignable;

                                    (e) The  number of  shares  of  "Registrable
Securities  then  outstanding"  shall be  determined  by the number of shares of
Common  Stock  outstanding  which are,  and the number of shares of Common Stock
issuable  pursuant to then  exercisable  or  convertible  securities  which are,
Registrable Securities; and
<PAGE>
                                    (f)  The  term  "Holder"  means  one  of the
Investors.

                           1.2      Shelf Registration.

                                    (a)  The  Company  shall,   subject  to  the
limitations  specified  in this  Agreement,  use its best  efforts (i) to file a
shelf  registration  statement  on Form S-3 or any other form  available  to the
Company  within  ninety  (90)  days from the date  hereof  (the  "Filing  Date")
covering  the  registration  under the Act of all  Registrable  Securities  then
outstanding  to be offered or sold on a delayed or continuous  basis as provided
by this  Agreement,  pursuant  to Rule 415 of the Act (the  "Shelf  Registration
Statement");  and (ii) to maintain the  effectiveness of the Shelf  Registration
Statement  for a period of two (2) years from the date this  Agreement  (or such
shorter period in accordance with Section 1.3).

                                    (b)  If any  offering  pursuant  to  Section
1.2(a) hereof involves an underwritten offering, an underwriter will be selected
by the Holders of two-thirds of the Registrable  Securities then outstanding and
shall be reasonably  acceptable to the Company.  In such event, the right of any
Holder to include  its  Registrable  Securities  in such  registration  shall be
conditioned  upon  such  Holder's  participation  in such  underwriting  and the
inclusion of such Holder's  Registrable  Securities in the  underwriting  to the
extent  provided  herein.  All  Holders  proposing  to  distribute   Registrable
Securities  through  such  underwriting  shall  (together  with the  Company  as
provided in Section  1.4(e)) enter into an  underwriting  agreement in customary
form  with the  underwriter  or  underwriters  selected  for such  underwriting.
Notwithstanding  any other  provision of this  Section  1.2, if the  underwriter
advises the Holders in writing that  marketing  factors  require a limitation of
the  number  of  shares  to be  underwritten,  then  the  number  of  shares  of
Registrable  Securities  that  may be  included  in the  underwriting  shall  be
allocated  among all Holders thereof in proportion (as nearly as practicable) to
the  amount of  Registrable  Securities  of the  Company  owned by each  Holder;
provided,  however,  that the number of shares of  Registrable  Securities to be
included in such  underwriting  shall not be reduced unless all Other Securities
(as defined below) are first entirely excluded from the underwriting.

                                    (c)  Notwithstanding  the foregoing,  if the
Company shall furnish to the Holders a certificate signed by the Chief Executive
Officer or President of the Company  stating that, in the good faith judgment of
the Board of  Directors of the Company,  it would be  seriously  detrimental  (a
"Detrimental  Condition") to the Company and its stockholders for a registration
statement to be filed or to become or remain effective,  as the case may be, and
provided that the  Detrimental  Condition has not resulted from actions taken by
the Company,  (i) the Company  shall have the right to defer taking  action with
respect to the filing of the Shelf  Registration  Statement  for a period of not
more  than  ninety  (90)  days  after  the  Filing  Date,  (ii)  in case a Shelf
Registration Statement has been filed but has not become effective,  the Company
may cause such  registration  statement to be withdrawn or may postpone amending
or supplementing such registration statement until such Detrimental Condition no
longer exists,  but in no event for more than ninety (90) days, or (iii) in case
a Shelf  Registration  Statement  has been filed and has become  effective,  the
Company  may  cause  such  registration   statement  to  be  withdrawn  and  its
effectiveness   terminated  or  may  postpone  amending  or  supplementing  such
registration statement until such Detrimental Condition no longer exists, but in
no event  for more  than  ninety  (90)  days.  The  Company  may not  declare  a
<PAGE>
Detrimental Condition, or take any of the actions specified in clauses (i), (ii)
or (iii) of the preceding  sentence (and can take only one such action specified
in clauses (i), (ii) or (iii) per Detrimental Condition),  more than once in any
twelve-month  period. The Company shall give written notice of its determination
to  postpone  or  withdraw  a  registration  statement  and of the fact that the
Detrimental  Condition for such  postponement or withdrawal no longer exists, in
each case,  promptly  after the  occurrence  thereof.  The  following  events or
circumstances  may  result  in the  filing  of a  registration  statement  being
seriously  detrimental to the Company and its  shareholders:  a pending material
acquisition,  merger  or sale or  purchase  of  assets,  pending  or  threatened
material  litigation,  pending or threatened material regulatory or governmental
action, pending material change in the business, prospects, condition (financial
or other) or properties of the Company.  The foregoing list is for  illustrative
purposes only and is not meant to be exclusive.

                                    (d) If the Company  shall give any notice of
postponement or withdrawal of any registration statement, the Company shall not,
during the period of postponement or withdrawal pursuant to clauses (i), (ii) or
(iii) of the prior paragraph,  register any Common Stock, other than pursuant to
a registration statement on Form S-4 or S-8 (or an equivalent  registration form
then in effect). Each Holder of Registrable Securities agrees that, upon receipt
of any notice from the Company that the Company has  determined  to withdraw any
registration  statement pursuant to the immediately  preceding  paragraph,  such
Holder will  discontinue its disposition of Registrable  Securities  pursuant to
such registration  statement and, if so directed by the Company, will deliver to
the Company (at the Company's  expense) all copies,  other than  permanent  file
copies,  then  in such  Holder's  possession  of the  prospectus  covering  such
Registrable Securities that was in effect at the time of receipt of such notice.
If the Company shall have  withdrawn or  prematurely  terminated a  registration
statement  filed under this  Section 1.2  (whether  pursuant to the  immediately
preceding paragraph, or as a result of any stop order, injunction or other order
or  requirement  of the SEC or any  other  governmental  agency or  court),  the
Company shall not be considered to have effected an effective  registration  for
the  purposes  of this  Agreement  until  the  Company  shall  have  filed a new
registration  statement  covering  the  Registrable  Securities  covered  by the
withdrawn registration statement and such registration statement shall have been
declared effective and shall not have been withdrawn.  If the Company shall give
any notice of  withdrawal  or  postponement  of a  registration  statement,  the
Company  shall,  at such time as the  Detrimental  Condition  that  caused  such
withdrawal or  postponement  no longer exists (but in no event later than ninety
(90)  days  after  the date of the  postponement  or  withdrawal),  use its best
efforts to effect the  registration  under the Securities Act of the Registrable
Securities  covered by the  withdrawn  or  postponed  registration  statement in
accordance  with this Section 1.2 (unless the Holder shall have  withdrawn  such
request,  in which case the Company  shall not be considered to have effected an
effective registration for the purposes of this Agreement).

                                    (e) Without the prior written consent of the
Holders of  two-thirds  of the  Registrable  Securities  then  outstanding,  the
registration  statement filed pursuant to this Section 1.2 may not include other
securities  of the  Company  (i) which  are held by  persons  who,  by virtue of
agreements  with the Company,  are entitled to include  their  securities in any
such registration, (ii) which are held by officers and directors of the Company,
or (iii) which are being  offered for the account of the Company  (collectively,
the securities  referred to in clauses (i), (ii) and (iii) in this paragraph are
hereinafter referred to as the "Other Securities").
<PAGE>
                           1.3  Company   Registration.   If  (but  without  any
obligation  to do so) the  Company  proposes  to  register  (including  for this
purpose a registration  effected by the Company for stockholders  other than the
Holders) any of its stock or other  securities  under the Act in connection with
the  public  offering  of  such  securities   solely  for  cash  (other  than  a
registration  relating  solely to the sale of  securities to  participants  in a
Company  stock  option,  stock  purchase  or  similar  plan  or a SEC  Rule  145
transaction, a registration on any form which does not include substantially the
same information as would be required to be included in a registration statement
covering the sale of the  Registrable  Securities or a registration in which the
only Common Stock being  registered is Common Stock issuable upon  conversion of
debt  securities  that are also being  registered),  the Company shall,  at such
time,  promptly give each Holder written notice of such  registration.  Upon the
written  request of each Holder given within  twenty (20) days after  mailing of
such notice by the Company in  accordance  with Section 2.5, the Company  shall,
subject to the provisions of Section 1.8,  cause to be registered  under the Act
all of the  Registrable  Securities  that each such Holder has  requested  to be
registered.  No registration effected pursuant to this Section 1.3 shall relieve
the Company of its obligations to effect the required  registration  pursuant to
Section  1.2.  Any  Holder  shall have the right to  withdraw  his  request  for
inclusion of its Registrable  Securities in any registration  statement pursuant
to this  Section 1.3 by giving  written  notice to the Company of its request to
withdraw.

                           1.4  Obligations of the Company.  When required under
this Section 1 to effect the  registration  of the Registrable  Securities,  the
Company shall, as expeditiously as reasonably possible:

                                    (a) Prepare and file with the Securities and
Exchange   Commission  (the  "SEC")  a  Shelf  Registration   Statement  or,  if
applicable,  any other form of registration  statement, as the case may be, with
respect to the  Registrable  Securities  and use its best  efforts to cause such
registration  statement to become effective within one hundred twenty (120) days
after such registration  statement was filed and to keep such Shelf Registration
Statement effective for a period up to the second anniversary of the date hereof
or until the distribution  contemplated in the Shelf Registration  Statement has
been completed;  provided,  however, that before filing a registration statement
or prospectus or any amendments or supplements thereto, or comparable statements
under securities or blue sky laws of any jurisdiction,  the Company will furnish
to one counsel for the Holders (the  "Holders'  Counsel")  participating  in the
planned  offering  (selected  by the Holders of  two-thirds  of the  Registrable
Securities   then   outstanding   included  in  such   registration),   and  the
underwriters,  if  any,  copies  of all  such  documents  proposed  to be  filed
(including  all  exhibits  thereto),  which  documents  will be  subject  to the
reasonable review and reasonable comment of such counsel.

                                    (b)  Prepare  and  file  with  the SEC  such
amendments  and  supplements to such  registration  statement and the prospectus
used in  connection  with such  registration  statement  as may be  necessary to
comply with the  provisions  of the Act with respect to the  disposition  of all
securities covered by such registration statement.

                                    (c) Furnish to the Holders whose Registrable
Securities  are  covered by the Shelf  Registration  Statement  such  numbers of
copies of a prospectus,  including a preliminary prospectus,  in conformity with
the  requirements  of the Act, and such other  documents as they may  reasonably
request in order to facilitate the disposition of Registrable  Securities  owned
by them.
<PAGE>
                                    (d) Use its best  efforts  to  register  and
qualify the securities  covered by such registration  statement under such other
securities  or Blue  Sky  laws of such  jurisdictions  as  shall  be  reasonably
requested by the Holders whose  Registrable  Securities are covered by the Shelf
Registration  Statement;  provided  that the  Company  shall not be  required in
connection  therewith or as a condition  thereto to qualify to do business or to
file a general consent to service of process in any such states or jurisdictions
unless the Company is already subject to service in such jurisdiction.

                                    (e) In the event the Registrable  Securities
are to be sold through an underwritten  public offering,  enter into and perform
its obligations  under an underwriting  agreement,  in usual and customary form,
with the  managing  underwriter  of such  offering.  The  Holders  proposing  to
distribute  Registrable  Securities  through such  underwritten  public offering
shall also enter into and perform their obligations under such an agreement.

                                    (f) In the event the Registrable  Securities
are to be sold through an underwritten public offering,  use its best efforts to
furnish,  on the date that such  Registrable  Securities  are  delivered  to the
underwriters for sale in connection with a registration pursuant to this Section
1, (i) an opinion,  dated such date, of the counsel representing the Company for
the purposes of such registration, in form and substance as is customarily given
to  underwriters  in  an  underwritten   public   offering,   addressed  to  the
underwriters, and (ii) a letter, dated such date, from the independent certified
public  accountants of the Company addressed to the  underwriters,  stating that
such accountants are independent  public  accountants  within the meaning of the
Act and the applicable published rules and regulations thereunder, and otherwise
in form and in substance as is customarily given by independent certified public
accountants to underwriters in connection with an underwritten public offering.

                                    (g) Promptly  notify (i) each Holder selling
Registrable  Securities covered by such registration statement and each managing
underwriter,  if any: (A) when the registration statement, the prospectus or any
prospectus  supplement  related  thereto  or  post-effective  amendment  to  the
registration  statement  has been filed and,  with  respect to the  registration
statement or any post-effective  amendment,  when the same has become effective,
(B) of the issuance by the SEC of any stop order suspending the effectiveness of
the  registration  statement  or the  initiation  of any  proceedings  for  that
purpose,  (C) of the receipt by the Company of any notification  with respect to
the suspension of the qualification of any Registrable Securities for sale under
the  securities or blue sky laws of any  jurisdiction  or the  initiation of any
proceeding  for  such  purpose,  and  (D)  when  a  prospectus  relating  to the
registration  statement  is  required  to be  delivered  under  the  Act  of the
happening  of any  event as a result of which the  prospectus  included  in such
registration  statement,  as then in effect,  includes an untrue  statement of a
material fact or omits to state a material fact required to be stated therein or
necessary  to make the  statements  therein not  misleading  in the light of the
circumstances  then  existing;  and (ii)  Holders'  Counsel  and  each  managing
underwriter  of any request by the SEC for  amendments  or  supplements  to such
registration   statement  or  prospectus   related  thereto  or  for  additional
information. If the notification relates to an event described in clause (i)(D),
the Company  shall,  in  accordance  with  paragraph  (b) of this  Section  1.4,
promptly  prepare  and  furnish to each Holder  selling  Registrable  Securities
covered by such registration statement and each managing underwriter,  if any, a
reasonable number of copies of a prospectus  supplemented or amended so that, as
<PAGE>
thereafter  delivered to the  purchasers of such  Registrable  Securities,  such
prospectus  shall not include an untrue  statement of a material fact or omit to
state a material  fact  required to be stated  therein or  necessary to make the
statements therein in the light of the circumstances  under which they were made
not misleading.

                                    (h)  Cooperate  with the selling  Holders of
Registrable  Securities and the managing underwriter,  if any, to facilitate the
timely  preparation  and delivery of  certificates  not bearing any  restrictive
legends  representing  the  Registrable  Securities  to be sold,  and cause such
Registrable Securities to be issued in such denominations and registered in such
names  in  accordance  with  the  underwriting  agreement  prior  to any sale of
Registrable  Securities to the underwriters or, if not an underwritten offering,
in  accordance  with the  instructions  of the  selling  Holders of  Registrable
Securities  at least  three  business  days  prior  to any  sale of  Registrable
Securities  and  instruct  any  transfer  agent  and  registrar  of  Registrable
Securities to release any stop transfer orders in respect thereto.

                                    (i)  Comply  with all  applicable  rules and
regulations of the SEC, and make generally available to its security holders, as
soon as  reasonably  practicable  after the effective  date of the  registration
statement (and in any event within 16 months thereafter),  an earnings statement
(which need not be audited)  covering the period of at least twelve  consecutive
months  beginning  with the first day of the Company's  first  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.

                                    (j)   (i)   Cause   all   such   Registrable
Securities covered by such registration  statement to be listed on the principal
securities  exchange on which similar  securities issued by the Company are then
listed (if any), if the listing of such Registrable Securities is then permitted
under the rules of such exchange,  or (ii) if no similar  securities are then so
listed,  to  either  cause  all such  Registrable  Securities  to be listed on a
national  securities  exchange or to secure  designation of all such Registrable
Securities as a National  Association  of  Securities  Dealers,  Inc.  Automated
Quotation System ("NASDAQ") "national market system security" within the meaning
of  Rule  11Aa2-1  of  the  Exchange  Act  or,   failing  that,   secure  NASDAQ
authorization  for such shares  and,  without  limiting  the  generality  of the
foregoing, take all actions that may be required by the Company as the issuer of
such  Registrable  Securities in order to facilitate the managing  underwriter's
arranging  for the  registration  of at least  two  market  makers  as such with
respect to such shares with the National Association of Securities Dealers, Inc.
(the "NASD").

                                    (k)  Provide  and cause to be  maintained  a
transfer agent and registrar for all such Registrable Securities covered by such
registration  statement not later than the effective  date of such  registration
statement.

                                    (l) Deliver promptly to Holders' Counsel and
each underwriter,  if any, copies of all correspondence  between the SEC and the
Company,  its counsel or auditors and all memoranda relating to discussions with
the SEC or its staff with  respect  to the  registration  statement,  other than
those  portions  of any such  memoranda  which  contain  information  subject to
attorney-client privilege with respect to the Company, and, upon receipt of such
confidentiality   agreements  as  the  Company  may  reasonably  request,   make
<PAGE>
reasonably available for inspection by Holders' Counsel, by any underwriter,  if
any,   participating  in  any  disposition  to  be  effected  pursuant  to  such
registration  statement and any attorney,  accountant or other agent retained by
any such  underwriter,  all  pertinent  financial and other  records,  pertinent
corporate  documents  and  properties  of  the  Company,  and  cause  all of the
Company's officers, directors and employees to supply all information reasonably
requested by Holders' Counsel or such underwriter, attorney, accountant or agent
in connection with such registration statement.

                                    (m) Use  reasonable  best  efforts to obtain
the withdrawal of any order  suspending the  effectiveness  of the  registration
statement.

                                    (n) Upon  written  request,  furnish to each
Holder  participating  in the  offering and the  managing  underwriter,  without
charge,  at least  one  conformed  copy of the  registration  statement  and any
post-effective amendments thereto, including financial statements and schedules,
all  documents  incorporated  therein by reference  and all exhibits  (including
those incorporated by reference).

                                    (o)  Take  all   such   other   commercially
reasonable  actions  as are  necessary  or  advisable  in order to  expedite  or
facilitate the disposition of such Registrable Securities.

                           1.5  Furnish  Information.  It shall  be a  condition
precedent to the  obligations of the Company to take any action pursuant to this
Section 1 with  respect  to the  Registrable  Securities  of the  Holders  whose
Registrable Securities are covered by the Shelf Registration Statement that each
of such Holders shall furnish to the Company such information  regarding itself,
the Registrable Securities held by it, and the intended method of disposition of
such securities as shall be required to effect the registration of such Holders'
Registrable Securities.

                           1.6 Expenses of Registration.

                                    (a)  "Expenses"  shall mean any and all fees
and expenses  incident to the Company's  performance of or compliance  with this
Article 1,  including,  without  limitation:  (i) SEC,  stock  exchange  or NASD
registration  and filing fees and all listing  fees and fees with respect to the
inclusion of  securities in NASDAQ,  (ii) fees and expenses of  compliance  with
state  securities or "blue sky" laws and in connection with the preparation of a
"blue sky" survey, including without limitation, reasonable fees and expenses of
blue sky  counsel,  (iii)  printing and copying  expenses,  (iv)  messenger  and
delivery expenses,  (v) expenses incurred in connection with any road show, (vi)
fees and  disbursements  of counsel for the Company,  (vii) with respect to each
registration,  the  fees  and  disbursements  of one  counsel  for  the  selling
Holder(s)  (selected by the Holders of two-thirds of the Registrable  Securities
then outstanding  included in such registration),  (viii) fees and disbursements
of the Company's  independent public accountants  (including the expenses of any
audit and/or  "cold  comfort"  letter) and fees and  expenses of other  persons,
including special experts,  retained by the Company,  (ix) any fees and expenses
payable  to a  Qualified  Independent  Underwriter  (as such term is  defined in
Conduct Rule 2720 of the National  Association  of  Securities  Dealers,  Inc.'s
By-Laws)  and (x) any other  fees and  disbursements  of  underwriters,  if any,
customarily paid by issuers or sellers of securities (collectively, "Expenses").
<PAGE>
                                    (b) The Company  shall pay all Expenses with
respect  to any  registration  pursuant  to  Section  1.2,  whether  or not such
registration  statement  becomes  effective or remains  effective for the period
contemplated by Section 1.2(a).

                                    (c) Notwithstanding  the foregoing,  (i) the
provisions of this Section 1.6 shall be deemed  amended to the extent  necessary
to cause these  expense  provisions to comply with "blue sky" laws of each state
in which  the  offering  is made and (ii) in  connection  with any  registration
hereunder,  each Holder of Registrable Securities being registered shall pay all
underwriting   discounts  and  commissions  and  any  transfer  taxes,  if  any,
attributable to the sale of such Registrable  Securities,  pro rata with respect
to payments of discounts and commissions in accordance with the number of shares
sold in the offering by such Holder, and (iii) the Company shall, in the case of
all  registrations  under this  Section 1, be  responsible  for all its internal
expenses  (including,  without  limitation,  all  salaries  and  expenses of its
officers and employees performing legal or accounting duties).

                           1.7  Expenses  of Company  Registration.  The Company
shall bear and pay all Expenses  incurred in  connection  with any  registration
filing  or  qualification   of  Registrable   Securities  with  respect  to  the
registrations  pursuant  to  Section  1.3 for each  Holder  (which  right may be
assigned as provided in Section 1.12), but excluding  underwriting discounts and
commissions relating to Registrable Securities.

                           1.8 Underwriting Requirements. In connection with any
offering involving an underwriting of shares of the Company's capital stock, the
Company  shall not be required  under Section 1.3 to include any of the Holders'
securities in such underwriting unless they accept the terms of the underwriting
as agreed upon  between the Company and the  underwriters  selected by it (or by
other  persons  entitled  to  select  the  underwriters),  and then only in such
quantity  as the  underwriters  determine  in  their  sole  discretion  will not
jeopardize  the success of the offering by the  Company.  If the total amount of
securities,  including Registrable  Securities,  requested by stockholders to be
included in such offering  exceeds the amount of  securities  sold other than by
the  Company  that the  underwriters  determine  in  their  sole  discretion  is
compatible with the success of the offering,  then the Company shall be required
to  include  in the  offering  only that  number of such  securities,  including
Registrable Securities, that the underwriters determine in their sole discretion
will not jeopardize  the success of the offering (the  securities so included to
be apportioned  pro rata among the selling  stockholders  according to the total
amount of  securities  entitled to be  included  therein  owned by each  selling
stockholder or in such other  proportions as shall mutually be agreed to by such
selling  stockholders)  but in no event  shall the amount of  securities  of the
selling  Holders  included in the offering be reduced below thirty percent (30%)
of the total amount of securities included in such offering. For purposes of the
preceding parenthetical  concerning  apportionment,  for any selling stockholder
that  is a  Holder  of  Registrable  Securities  and  that is a  partnership  or
corporate  partners,  retired partners and  stockholders of such Holder,  or the
estates and family  members of any such  partners  and retired  partners and any
trusts for the benefit of any of the  foregoing  persons shall be deemed to be a
single "selling  stockholder,"  and any pro-rata  reduction with respect to such
"selling  stockholder"  shall  be based  upon the  aggregate  amount  of  shares
carrying  registration rights owned by all entities and individuals  included in
such "selling stockholder," as defined in this sentence.
<PAGE>
                           1.9 Delay of Registration. The Holders shall not have
any right to obtain or seek an injunction  restraining or otherwise delaying any
such registration as the result of any controversy that might arise with respect
to the interpretation or implementation of this Section 1.

                           1.10  Indemnification.  In the event any  Registrable
Securities are included in a registration statement under this Section 1:

                                    (a) To the  extent  permitted  by  law,  the
Company will indemnify and hold harmless the Holder whose Registrable Securities
are covered by the Registration Statement, its directors, officers, fiduciaries,
employees and  stockholders  or general or limited  partners (and the directors,
officers,  employees and stockholders  thereof),  any underwriter (as defined in
the Act) for such Holders and each person,  if any, who controls such Holders or
underwriter  within the  meaning of the Act or the  Securities  Exchange  Act of
1934, as amended (the "1934 Act"), each officer, director, employee, stockholder
or  partner  of such  underwriter,  against  any  losses,  claims,  damages,  or
liabilities  (joint or several) or actions or proceedings  (whether commenced or
threatened) and expenses  (including  reasonable fees of counsel and any amounts
paid in any settlement effected with the Company's  consent),  to which they may
become subject under the Act, the 1934 Act or any state  securities law, insofar
as such losses,  claims,  damages,  or liabilities (or actions or proceedings in
respect  thereof)  ("Claims") or expenses  arise out of or are based upon any of
the following statements,  omissions or violations (collectively a "Violation"):
(i) any  untrue  statement  or  alleged  untrue  statement  of a  material  fact
contained in such registration statement,  including any preliminary prospectus,
summary  prospectus or final prospectus  contained  therein or any amendments or
supplements thereto,  together with documents incorporated by reference therein,
(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 the Company of the
Act,  the  1934  Act,  any  state  securities  law or  any  rule  or  regulation
promulgated  under the Act,  the 1934 Act or any state  securities  law; and the
Company  will pay to such  Holders,  and each such  underwriter  or  controlling
person any legal or other  expenses  reasonably  incurred by them in  connection
with investigating or defending any such loss, claim, damage, liability, expense
or action or proceeding;  provided,  however,  that (A) the indemnity  agreement
contained in this Section 1.10 shall not apply to amounts paid in  settlement of
any such Claim if such settlement is effected without the consent of the Company
(which consent shall not be unreasonably withheld), (B) the Company shall not be
liable in any case for any such Claim 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 any such Holders, or any such underwriter or controlling person.
Such  indemnity  and  reimbursement  of expenses  shall remain in full force and
effect regardless of any investigation  made by as on behalf of such indemnified
party and shall survive the transfer of such securities by such Holder.

                                    (b) To the  extent  permitted  by law,  each
Holder  whose  Registrable  Securities  are  covered  by the Shelf  Registration
Statement  will,  severally  and not jointly,  indemnify  and hold  harmless the
Company,  each  of its  directors,  each of its  officers  who  has  signed  the
registration statement, each person, if any, who controls the Company within the
meaning of the Act,  any  underwriter,  and any  controlling  person of any such
underwriter,  against any losses,  claims,  damages,  or  liabilities  (joint or
several) to which any of the  foregoing  persons may become  subject,  under the
Act, or the 1934 Act,  insofar as such Claim  arises out of or is based upon any
<PAGE>
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 such Holder expressly for use in connection with such registration;
and such Holder will pay, as incurred,  any legal or other  expenses  reasonably
incurred by any person intended to be indemnified pursuant to this Section 1.10,
in connection with investigating or defending any such Claim; provided, however,
that the indemnity  agreement  contained in this Section 1.10 shall not apply to
amounts  paid in  settlement  of any such Claim if such  settlement  is effected
without the consent of such  Holder,  which  consent  shall not be  unreasonably
withheld; provided that, in no event shall any indemnity under this Section 1.10
exceed  the net  proceeds  from  the  offering  received  by such  Holder.  Such
indemnity and  reimbursement  of expenses  shall remain in full force and effect
regardless of any  investigation  made by as on behalf of such indemnified party
and shall survive the transfer of such securities by such Holder.

                                    (c) Promptly after receipt by an indemnified
party  under  this  Section  1.10 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
1.10,  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  (together  with all other  indemnified  parties which may be  represented
without  conflict by one  counsel)  shall have the right to retain one  separate
counsel, with the fees and expenses to be paid by the indemnifying party, (i) 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;  (ii) if the  indemnifying  party  fails  to take
reasonable steps necessary to defend  diligently the action or proceeding within
30 days after  receiving  notice from such  indemnified  party; or (iii) if such
indemnified  party who is a defendant in any action or proceeding  which is also
brought  against the  indemnifying  party  reasonably  shall have concluded that
there may be one or more legal  defenses  available  to such  indemnified  party
which are not  available  to the  indemnifying  party.  The  failure  to deliver
written  notice  to the  indemnifying  party  within  a  reasonable  time of the
commencement  of any such action,  if  prejudicial to its ability to defend such
action,   shall  relieve  such  indemnifying  party  of  any  liability  to  the
indemnified  party  under this  Section  1.10,  but the  omission  so 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
1.10.

                                    (d) If the  indemnification  provided for in
this Section 1.10 is held by a court of competent jurisdiction to be unavailable
to an  indemnified  party  with  respect  to any Claim or  expense  referred  to
therein,  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 Claim or expense in such proportion as is
appropriate to reflect the relative fault of the  indemnifying  party on the one
hand and of the indemnified party on the other in connection with the statements
or  omissions  that  resulted  in such  Claim or  expense  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
<PAGE>
things, whether the untrue or alleged untrue statement of a material fact or the
omission  to state a  material  fact  relates  to  information  supplied  by the
indemnifying party or by the indemnified party and the parties' relative intent,
knowledge,  access to  information,  and  opportunity to correct or prevent such
statement  or  omission.  If,  however,  the  allocation  provided  in the first
sentence  of this  paragraph  is not  permitted  by  applicable  law,  then each
indemnifying  party  shall  contribute  to the  amount  paid or  payable by such
indemnified  party in such proportion as is appropriate to reflect not only such
relative faults but also the relative benefits of the indemnifying party and the
indemnified party as well as any other relevant  equitable  considerations.  The
parties  hereto agree that it would not be just and  equitable if  contributions
pursuant to this Section 1.10(d) were to be determined by pro rata allocation or
by any other method of  allocation  which does not take account of the equitable
considerations  referred to in the preceding  sentences of this Section 1.10(d).
The amount  paid or  payable in respect of any Claim  shall be deemed to include
any legal or other expenses  reasonably  incurred by such  indemnified  party in
connection  with  investigating  or defending  such Claim.  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.  Notwithstanding  anything in this
Section 1.10(d) to the contrary,  no indemnifying party (other than the Company)
shall be required  pursuant to this Section  1.10(d) to contribute any amount in
excess of the net proceeds received by such indemnifying  party from the sale of
Registrable  Securities  in the offering to which the Claims of the  indemnified
parties  relate,  less the amount of any  indemnification  payment  made by such
indemnifying party pursuant to Sections 1.10(b).

                                    (e)  Notwithstanding  the foregoing,  to the
extent that the provisions on indemnification and contribution  contained in the
underwriting  agreement entered into in connection with the underwritten  public
offering are in conflict with the foregoing  provisions,  the  provisions in the
underwriting agreement shall control.

                                    (f)  The  obligations  of  the  Company  and
Holders under this Section 1.10 shall survive the  completion of any offering of
Registrable  Securities in a  registration  statement  under this Section 1, and
otherwise.

                           1.11 Reports Under  Securities  Exchange Act of 1934.
With a view to  making  available  to the  Holders  the  benefits  of  Rule  144
promulgated  under the Act and any other rule or  regulation of the SEC that may
at any time  permit a Holder to sell  securities  of the  Company  to the public
without  registration  or pursuant to a  registration  on Form S-3,  the Company
agrees to:

                                    (a)  make  and   keep   public   information
available,  as those  terms are  understood  and defined in SEC Rule 144, at all
times;

                                    (b) take  such  action  as is  necessary  to
maintain  the  Holder's  ability  to  utilize  Form  S-3 for the  sale of  their
Registrable Securities;

                                    (c) file with the SEC in a timely manner all
reports and other  documents  required of the Company under the Act and the 1934
Act; and
<PAGE>
                                    (d)  furnish to any  Holder,  so long as the
Holder owns any  Registrable  Securities,  forthwith  upon request (i) a written
statement by the Company that it has complied with the reporting requirements of
SEC Rule 144, the Act and the 1934 Act (at any time after it so qualifies), (ii)
a copy of the most  recent  annual or  quarterly  report of the Company and such
other  reports and  documents  filed by the Company with the SEC, and (iii) such
other  information as may be reasonably  requested in availing any Holder of any
rule or regulation  of the SEC which permits the selling of any such  securities
without registration or pursuant to such form.


                           1.12     Assignment of Registration Rights.

                                    (a) The  rights  to  cause  the  Company  to
register Registrable  Securities pursuant to this Section 1 may be assigned (but
only with all related  obligations)  by a Holder to a transferee or assignees of
such  securities  who  acquires  at least two  percent  (2%) of the  Registrable
Securities (as adjusted for stock splits,  combinations and the like), provided:
(i) the Company is, within a reasonable time after such transfer, furnished with
written  notice of the name and address of such  transferee  or assignee and the
securities  with respect to which such  registration  rights are being assigned;
(ii) such transferee or assignee agrees in writing to be bound by and subject to
the terms and conditions of this Agreement,  including,  without limitation, the
provisions of Section 1.14 below;  and (iii) such assignment  shall be effective
only if such  transfer  is  exempt  from  registration  under  the Act.  For the
purposes of determining the number of shares of Registrable Securities held by a
transferee  or  assignee,   the  holding  of  transferees  and  assignees  of  a
partnership who are partners or retired partners of such partnership  (including
spouses and  ancestors,  lineal  descendants  and  siblings of such  partners or
spouses  who  acquire   Registrable   Securities  by  gift,  will  or  intestate
succession) shall be aggregated together with the partnership; provided that all
assignees and transferees who would not qualify  individually  for assignment of
registration  rights  shall have a single  attorney-in-fact  for the  purpose of
exercising any rights, receiving notices or taking any action under this Section
1.

                                    (b)  Subject to clause (a) above,  the right
to have the Company register the Registrable Securities pursuant to this Section
1 may not  otherwise be assigned;  provided,  however,  that (i) any heir or the
estate of an  Investor  which  acquires  the  Registrable  Securities  from such
Investor by will or intestate  succession  shall be entitled to have the Company
register the  Registrable  Securities  pursuant to this Section 1 (provided that
such heirs or such estate shall have a single  attorney-in-fact  for the purpose
of exercising any rights,  receiving any notices or taking any action under this
Section  1),  and (ii) any  individual  Investor  may sell,  assign or  transfer
Registrable  Securities  to  his  or  her  spouse  or  children  or  to a  trust
established  for the  benefit  of his or her  spouse,  children  or  himself  or
herself,  and such transferee shall be entitled to have the Company register the
Registrable  Securities  pursuant  to this  Section  1, if,  and  only if,  such
transferee agrees in writing to be bound by the terms of this Agreement. In each
such event and for purposes of this Agreement,  the term "Holder" as used herein
shall include all such heirs, such estate or such transferees.
<PAGE>
                           1.13 Limitations on Subsequent  Registration  Rights.
From and after the date of this  Agreement,  the Company shall not,  without the
prior written consent of the Holders of two-thirds of the Registrable Securities
then outstanding, enter into any agreement with any holder or prospective holder
of any  securities  of the Company  that would allow such holder or  prospective
holder (a) to include such  securities in any  registration  filed under Section
1.2 hereof, unless under the terms of such agreement, such holder or prospective
holder may include such securities in any such  registration  only to the extent
that  the  inclusion  of his  securities  will  not  reduce  the  amount  of the
Registrable  Securities  of the Holders that is included or (b) to make a demand
registration  that could result in such  registration  statement  being declared
effective  within one hundred  twenty  (120) days of the  effective  date of any
registration effected pursuant to Section 1.2.

                           1.14  "Market  Stand-Off"  Agreement.  Each  Investor
hereby agrees that,  during the period of duration  specified by the Company and
an underwriter of Common Stock or other securities of the Company, following the
effective date of a  registration  statement of the Company filed under the Act,
it shall not,  to the extent  requested  by the  Company  and such  underwriter,
directly or indirectly sell, offer to sell, contract to sell (including, without
limitation,  any short sale), grant any option to purchase or otherwise transfer
or  dispose  of (other  than to  donees  who agree to be  similarly  bound)  any
securities  of the Company  held by it at any time  during  such  period  except
Common Stock included in such  registration,  and each Investor  agrees to enter
into an agreement to such effect with such underwriter;  provided, however, that
(a) all officers and  directors  of the Company  enter into similar  agreements,
and, (b) such market  stand-off  time period  shall not exceed 120 days.  If the
underwriters agree to any waivers of such restrictions, then the Investors shall
be  entitled  to sell,  transfer  or  dispose  of the same  number  or amount of
securities of the Company as the person or entity  receiving  such waiver,  upon
the same terms and conditions set forth in such waiver.

                           In order  to  enforce  the  foregoing  covenant,  the
Company may impose  stop-transfer  instructions  with respect to the Registrable
Securities of the Investors  (and the shares or securities of every other person
subject to the foregoing restriction) until the end of such period.

                           1.15 No  Required  Sale.  Nothing  in this  Agreement
shall be deemed to create an independent obligation on the part of any Holder to
sell  any  Registrable   Securities  pursuant  to  any  effective   registration
statement.

                  2.       Miscellaneous.

                           2.1  Successors  and  Assigns.  Except  as  otherwise
provided  herein,  and provided that the transfer or assignment is in accordance
with the terms hereof, the terms and conditions of this Agreement shall inure to
the benefit of and be binding upon the respective  successors and assigns of the
parties  (including  any  permitted  transferees  of any  shares of  Registrable
Securities).  Nothing in this  Agreement,  express or  implied,  is  intended to
confer  upon  any  party  other  than the  parties  hereto  or their  respective
successors and assigns any rights, remedies,  obligations,  or liabilities under
or by reason of this Agreement, except as expressly provided in this Agreement.

                           2.2 Governing Law. This  Agreement  shall be governed
by and  construed  under  the laws of the  State of New York  without  regard to
principles of conflicts or choice of laws.
<PAGE>
                           2.3  Counterparts.  This Agreement may be executed in
two or more counterparts,  each of which shall be deemed an original, but all of
which together shall constitute one and the same instrument.

                           2.4 Titles and  Subtitles.  The titles and  subtitles
used  in  this  Agreement  are  used  for  convenience  only  and  are not to be
considered in construing or interpreting this Agreement.

                           2.5 Notices.  Unless otherwise  provided,  any notice
required or permitted  under this Agreement  shall be given in writing and shall
be deemed  effectively  given upon personal delivery to the party to be notified
or upon deposit with the United  States Post Office,  by registered or certified
mail,  postage  prepaid and addressed to the party to be notified at the address
indicated  for such  party in the Stock  Purchase  Agreement,  or at such  other
address as such party may designate by ten (10) days' advance  written notice to
the other parties.

                           2.6  Expenses.  If any  action at law or in equity is
necessary to enforce or interpret the terms of this  Agreement,  the  prevailing
party shall be entitled  to  reasonable  attorneys'  fees,  costs and  necessary
disbursements  in  addition  to any  other  relief  to which  such  party may be
entitled.

                           2.7  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),  only with the written consent of the Company and the Holders of
two-thirds of the  Registrable  Securities  then  outstanding.  Any amendment or
waiver  effected in accordance  with this Section 2.7 shall be binding upon each
Holder of any Registrable Securities then outstanding, each future Holder of all
such Registrable Securities, and the Company.

                           2.8  Severability.  If one or more provisions of this
Agreement are held to be  unenforceable  under  applicable  law, such  provision
shall be excluded from this Agreement and the balance of the Agreement  shall be
interpreted  as if such  provision  were so excluded and shall be enforceable in
accordance with its terms.

                           2.9 Nominees for  Beneficial  Owners.  If Registrable
Securities  are  held  by a  nominee  for  the  beneficial  owner  thereof,  the
beneficial  owner  thereof may, at its option,  be treated as the Holder of such
Registrable Securities for purposes of any request or other action by any Holder
or  Holders  of  Registrable  Securities  pursuant  to  this  Agreement  (or any
determination  of any number or  percentage of shares  constituting  Registrable
Securities held by any Holder or Holders of Registrable Securities  contemplated
by this  Agreement),  provided that the Company  shall have received  assurances
reasonably satisfactory to it of such beneficial ownership.

                           2.10  Specific   Performance.   The  parties   hereto
acknowledge  that there would be no adequate remedy at law if any party fails to
perform any of its obligations hereunder, and accordingly agree that each party,
in addition to any other remedy to which it may be entitled at law or in equity,
shall be entitled to  injunctive  relief,  including  specific  performance,  to
enforce  such  obligations  without the posting of any bond,  and, if any action
should be brought in equity to enforce any of the provisions of this  Agreement,
none of the parties  hereto  shall  raise the defense  that there is an adequate
remedy at law.
<PAGE>
                           2.11 No Inconsistent  Agreements.  The rights granted
to the Holders of  Registrable  Securities  hereunder do not in any way conflict
with and are not inconsistent  with any other agreements to which the Company is
a party or by which it is  bound.  Without  the  prior  written  consent  of the
holders of two-thirds of the Registrable  Securities then  outstanding,  neither
the Company nor any Holder will, on or after the date of this  Agreement,  enter
into any agreement with respect to its securities which is inconsistent with the
rights  granted in this  Agreement or otherwise  conflicts  with the  provisions
hereof,  other than any lock-up  agreement with the  underwriters  in connection
with any registered offering effected  hereunder,  pursuant to which the Company
shall agree not to register for sale, and the Company shall agree not to sell or
otherwise  dispose  of,  Common  Stock  or any  securities  convertible  into or
exercisable or exchangeable  for Common Stock,  for a specified period following
the  registered  offering.   The  Company  further  agrees  that  if  any  other
registration rights agreement entered into after the date of this Agreement with
respect to any of its securities  contains terms which are more favorable to, or
less  restrictive  on, the other party thereto than the terms and  conditions in
this  Agreement are (insofar as they are  applicable  to the Holders),  then the
terms and conditions of this Agreement shall  immediately be deemed to have been
amended  without  further  action  by the  Company  or any  of  the  Holders  of
Registrable  Securities  so that the Holders shall be entitled to the benefit of
any such more favorable or less restrictive terms or conditions.

                           2.12 Entire Agreement.  This Agreement (including the
Exhibits  hereto,  if any)  constitutes  the full and entire  understanding  and
agreement between the parties with regard to the subjects hereof and thereof.




<PAGE>



                  IN  WITNESS   WHEREOF,   the  parties   have   executed   this
Registration Rights Agreement as of the date first above written.


   


                                 EXOGEN, INC.    
                                                
                                                       
                                                                
                                 By:    /s/ Patrick A. McBrayer 
                                        ----------------------- 
                                 Name:  Patrick A. McBrayer     
                                 Title: President and Chief Executive Officer 
                                                                     
                                 Address:      10 Constitution Avenue           
                                               P.O. Box 6860          
                                               Piscataway, NJ 08855  
                                                       
                                                                                
                                 INVESTORS:                                     
                                                                                
                                 DELPHI VENTURES III, L.P.                      
                                                                                
                                 By:     Delphi Management Partners III, L.L.C.,
                                         General Partner                        
                                                                                
                                                   
                                 By:     /s/ Donald J. Lothrop 
                                         --------------------- 
                                 Name:   Donald J. Lothrop                      
                                 Title:  Managing Member                        
                                                                                
                                                                                
                                 DELPHI BIO-INVESTMENTS III, L.P.               
                                                                                
                                 By:     Delphi Management Partners III, L.L.C.,
                                         General Partners                       
                                                                                
                                                                                
                                 By:     /s/ Donald J. Lothrop                  
                                         ---------------------                  
                                 Name:   Donald J. Lothrop                      
                                 Title:  Managing Member 
                       
                                                                                
                         






                          REGISTRATION RIGHTS AGREEMENT
                                 
<PAGE>



                                   THE DEMETER TRUST DTD 6/5/90
                                   TRUSTEE


                                   By:   /s/ Richard Johnston
                                         --------------------
                                   Name: Richard Johnston



                                   ALEXANDRA F. JOHNSTON TRUST DTD
                                   11/6/78
                                   Trustee

                                   By:   /s/ Richard Johnston
                                         --------------------
                                   Name: Richard Johnston



                                   BRADFORD D. JOHNSTON TRUST DTD
                                   11/6/78
                                   Trustee

                                   By:   /s/ Richard Johnston
                                         --------------------
                                   Name: Richard Johnston



                                   WILLIAM M. JOHNSTON TRUST DTD
                                   11/6/7
                                   Trustee

                                   By:   /s/ Richard Johnston
                                         --------------------
                                   Name: Richard Johnston



                                   ROBERT F. JOHNSTON


                                   By: /s/ Robert F. Johnston
                                       ----------------------
                                       Robert F. Johnston







                          REGISTRATION RIGHTS AGREEMENT

<PAGE>




                                   PEQUOT PRIVATE EQUITY FUND L.P.


                                   By:      /s/ Amiel Peretz
                                            ----------------
                                   Name:    Amiel Peretz
                                   Title:   CFO, DSCMI Inv. Mgr.


                                   PEQUOT OFFSHORE PRIVATE EQUITY
                                   FUND, INC.


                                   By:      /s/ Amiel Peretz
                                            ------------------
                                   Name:    Amiel Peretz
                                   Title:   CFO, DSCMI Inv. Mgr.




                          REGISTRATION RIGHTS AGREEMENT

<PAGE>





                           PIPER JAFFRAY HEALTHCARE CAPITAL
                           LIMITED PARTNERSHIP (SBIC)

                           By:      Piper Ventures Management IV Limited
                                    Partnership, its General Partner


                           By:      /s/ Buzz Benson
                                    ---------------
                                    Buzz Benson, Managing Director Piper
                                    Ventures Capital, Inc., Its General Partner




                          REGISTRATION RIGHTS AGREEMENT

<PAGE>



                                   TERENCE D. WALL


               
                                   By: /s/ Terence D. Wall
                                       -------------------
                                       Terence D. Wall


                          REGISTRATION RIGHTS AGREEMENT