EXHIBIT 10.18















                                  EXOGEN, INC.


                         COMMON STOCK PURCHASE AGREEMENT



                                October 20, 1997



<PAGE>
                                TABLE OF CONTENTS

                                                                                

         1.       Purchase and Sale of Stock....................................
                  1.1      Sale and Issuance of Common Stock....................
                  1.2      Closing..............................................
                  1.3      Actions at the Closing...............................

         2.       Representations and Warranties of the Company.................
                  2.1      Organization and Good Standing; Power and Authority;
                               Qualifications...................................
                  2.2      Authorization........................................
                  2.3      Capitalization.......................................
                  2.4      Valid Issuance of Common Stock.......................
                  2.5      Consents.............................................
                  2.6      Litigation...........................................
                  2.7      Compliance with Other Instruments....................
                  2.8      Financial Statements.................................
                  2.9      SEC Filings..........................................
                  2.10     Other Information....................................
                  2.11     Intellectual Property Rights.........................
                  2.12     Title to Assets and Properties; Insurance............
                  2.13     Compliance with Laws; Permits........................
                  2.14     Offering Exemption...................................
                  2.15     Taxes................................................

         3.       Representations and Warranties of the Investor................
                  3.1      Authorization........................................
                  3.2      Purchase Entirely for Own Account....................
                  3.3      Disclosure of Information............................
                  3.4      Investment Experience................................
                  3.5      Accredited Investor..................................
                  3.6      Restricted Securities................................

         4.       Certain Covenants.............................................
                  4.1      Use of Proceeds......................................
                  4.2      Rule 144 Reporting...................................

         5.       Transfer Taxes................................................

         6.       Expenses......................................................

         7.       Indemnification...............................................
                  7.1      General Indemnification..............................
                  7.2      Indemnification Principles...........................
                  7.3      Claim Notice.........................................

         8.       Remedies......................................................
<PAGE>
         9.       Miscellaneous.................................................
                  9.1      Survival of Warranties...............................
                  9.2      Successors and Assigns...............................
                  9.3      Governing Law........................................
                  9.4      Counterparts.........................................
                  9.5      Titles and Subtitles.................................
                  9.6      Notices..............................................
                  9.7      Finder's Fee.........................................
                  9.8      Attorneys' Fees......................................
                  9.9      Amendments and Waivers...............................
                  9.10     Severability.........................................
                  9.11     Entire Agreement.....................................
                  9.12     Press Releases and Announcements.....................



SCHEDULE 1    -   List of Investors, addresses, number of shares of Common Stock
                  being purchased and purchase price due from each Investor

EXHIBIT A     -   Registration Rights Agreement

EXHIBIT B-1   -   Certificate for Individual Investors

EXHIBIT B-2   -   Certificate for Corporate, Partnership, Trust, Foundation and 
                  Joint Investors

EXHIBIT C     -   Secretary's Certificate

EXHIBIT D     -   Opinion of Brobeck, Phleger & Harrison LLP
<PAGE>
                         COMMON STOCK PURCHASE AGREEMENT
                         -------------------------------


                  THIS STOCK  PURCHASE  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 attached  hereto,  each of
which is herein referred to as an "Investor".

                  THE PARTIES HEREBY AGREE AS FOLLOWS:

                  1.       Purchase and Sale of Stock.

                  1.1 Sale and  Issuance of Common  Stock.  Subject to the terms
and  conditions  of this  Agreement,  each  Investor  agrees to  purchase at the
Closing and the Company agrees to sell and issue to the Investor at the Closing,
that number of shares of the Company's common stock,  $.0001 par value per share
("Common  Stock"),  and at a purchase price per share,  as is set forth opposite
each Investor named on Schedule 1 attached hereto (such transaction  referred to
as the "Purchase").  The maximum aggregate number of shares of Common Stock sold
pursuant  to this  Agreement  shall  be One  Million  Nine  Hundred  Eighty-Nine
Thousand Six Hundred Thirty (1,989,630) shares.

                  1.2  Closing.  The purchase and sale of the Common Stock shall
take place at the offices of Brobeck,  Phleger & Harrison  LLP,  1633  Broadway,
47th floor,  New York,  New York 10019 at 10:00 a.m. New York Time,  on the date
hereof,  or at such time and place upon which the  Company and  Investors  shall
agree  (the  "Closing").  At the  Closing,  the  Company  shall  deliver to each
Investor a certificate or certificates  representing the Common Stock which such
Investor is purchasing,  registered in the name of such Investor or its nominee,
against payment of the purchase price therefor by wire transfer to the Company's
bank account  (designated at least one business day prior to the Closing) in the
amount set forth on Schedule 1.

                  1.3. Actions at the Closing. Simultaneously with, or prior to,
the execution and delivery of this Agreement, the following actions shall occur:

                           (a)   The   Registration    Rights   Agreement   (the
"Registration Rights Agreement"),  by and between the Company and the Investors,
substantially  in the  form  of  Exhibit  A  hereto,  and all  other  schedules,
certificates  and other documents  being delivered  pursuant to or in connection
with  this   Agreement   by  any  party  hereto  at  or  prior  to  the  Closing
(collectively,  the "Ancillary  Documents") shall be duly executed and delivered
by the parties thereto.

                           (b)  The  Company  shall  deliver  to  the  Investors
certificates  of good  standing  from the  jurisdictions  set forth on  Schedule
1.3(b)  under its name dated as of a date no earlier than five days prior to the
Closing.

                           (c) The  Common  Stock to be issued  shall  have been
approved for listing on The NASDAQ Stock Market,  subject to official  notice of
issuance.
<PAGE>
                           (d) The  Investors  shall  deliver  to the  Company a
completed  certificate  pertaining  to such  Investor's  status  as an  investor
substantially in the form of Exhibit B-1 or B-2, as appropriate.

                           (e) The  Company  shall  deliver to the  Investors  a
certificate executed by the secretary of the Company,  substantially in the form
of  Exhibit  C hereto,  certifying  (i) a copy of its  organizational  documents
(including the  Certificate of  Incorporation  and bylaws of the Company),  (ii)
resolutions authorizing the transaction and (iii) incumbency matters.

                           (f) The Investors shall receive from Brobeck, Phleger
& Harrison LLP, counsel for the Company,  an opinion addressed to the Investors,
dated as of the Closing,  satisfactory  in form and substance to the  Investors,
which shall include the opinions set forth in Exhibit D attached hereto.

                  2.  Representations and Warranties of the Company. The Company
hereby represents and warrants to the Investor that:

                  2.1  Organization  and Good  Standing;  Power  and  Authority;
Qualifications.  Each of the Company and its subsidiary, Exogen (Europe) GmbH, a
German  corporation (the  "Subsidiary") (i) is duly organized,  validly existing
and in good standing under the laws of its jurisdiction of organization and (ii)
has all requisite  power and authority to own,  lease and operate its properties
and to carry on its  business  as  presently  conducted  and as  proposed  to be
conducted.  The Company has all requisite  power and authority to enter into and
carry out the  transactions  contemplated  by this  Agreement  and the Ancillary
Documents  to which it is a party.  Each of the  Company and its  Subsidiary  is
qualified  to  transact  business  as a foreign  corporation  in, and is in good
standing  under the laws of,  those  jurisdictions  that  constitute  all of the
jurisdictions  wherein  the  character  of the  property  owned or leased or the
nature of the activities conducted by it makes such qualification  necessary and
where  failure to so  qualify  would  individually  or in the  aggregate  have a
material  adverse  effect  on  properties,   business,  prospects,   operations,
earnings,  assets,  liabilities or the condition (financial or otherwise) of the
Company  and its  Subsidiary  taken as a whole,  whether or not in the  ordinary
course of business (a "Material Adverse Effect").  All of the outstanding shares
of capital  stock of each class (other than director  qualifying  shares) of the
Subsidiary  have been validly issued and fully paid and  nonassessable,  and are
owned   beneficially  and  of  record,  by  the  Company,   free  and  clear  of
Encumbrances.

                  2.2  Authorization.  All  corporate  action on the part of the
Company,   its   officers,   directors  and   shareholders   necessary  for  the
authorization,  execution  and  delivery  of this  Agreement  and the  Ancillary
Documents,  the  performance  of all  obligations  of the Company  hereunder and
thereunder  and the  authorization,  issuance  and  delivery of the Common Stock
being sold  hereunder  has been  taken,  and this  Agreement  and the  Ancillary
Documents,  constitute  valid and legally  binding  obligations  of the Company,
enforceable  against  the Company in  accordance  with their  respective  terms,
except (i) as  limited by  applicable  bankruptcy,  insolvency,  reorganization,
moratorium,  and other  laws of general  application  affecting  enforcement  of
creditors'  rights   generally,   (ii)  as  limited  by  laws  relating  to  the
availability  of specific  performance,  injunctive  relief,  or other equitable
remedies,  and (iii) to the extent the indemnification  provisions  contained in
the Registration  Rights Agreement may be limited by applicable federal or state
securities laws.
<PAGE>
                  2.3  Capitalization.  The  authorized  capitalization  of  the
Company immediately following the Purchase will consist of: (a) 3,000,000 shares
of preferred stock of the Company (the "Preferred Stock"),  par value $.0001 per
share, of which no shares are issued and outstanding;  and (b) 27,000,000 shares
of Common Stock, par value $.0001 per share ("Common Stock"), of which 9,998,140
shares are issued and  outstanding and all such  outstanding  shares are validly
issued,  fully paid and nonassessable and free and clear of all Encumbrances (as
defined in Section  2.12).  No class of capital stock  ("Capital  Stock") of the
Company is entitled to  preemptive  rights.  There are no  outstanding  options,
warrants,  subscription rights, calls or commitments of any character whatsoever
relating to, or securities or rights  convertible  into,  shares of any class of
Capital  Stock of the  Company,  or  contracts,  by  which  the  Company  or its
Subsidiary  is or may become  bound to issue  additional  shares of its  Capital
Stock or options,  warrants or other rights to purchase or acquire any shares of
its Capital  Stock,  except as follows:  (i) 750,000 shares of Common Stock have
been  reserved for issuance  pursuant to the Company's  1995 Stock  Option/Stock
Issuance Plan (of which options to purchase  632,973 shares of Common Stock have
been granted and are outstanding), (ii) 150,000 shares of Common Stock have been
reserved for issuance pursuant to the Company's Employee Stock Purchase Plan (of
which  95,940  shares of Common  Stock have been  purchased  and are included in
total  shares of Common Stock  outstanding),  and (iii) as set forth on Schedule
2.3, shares of Common Stock reserved for issuance  pursuant to a certain warrant
to purchase Common Stock of the Company and certain warrant obligations.  Except
as set forth in Schedule  2.3 hereto,  the Company has not  declared or paid any
dividend or made any other  distribution of cash, stock or other property to its
stockholders.

                  2.4 Valid Issuance of Common Stock.  The Common Stock which is
being purchased by each Investor  hereunder,  when issued, sold and delivered in
accordance with the terms hereof for the consideration expressed herein, will be
duly and validly issued and outstanding,  fully paid and  nonassessable  with no
personal  liability  attaching to the ownership  thereof,  free and clear of any
Encumbrances,  other than  Encumbrances,  if any, arising as a result of actions
taken by the  Investors,  and not  subject to  preemptive  or similar  rights of
stockholders of the Company or others.

                  2.5  Consents.  Except as disclosed on Schedule 2.5 hereto and
for  any  post-Closing  notifications  or  filings  as  may  be  required  under
applicable  federal or state  securities  laws, if any, which shall be made on a
timely basis, no consent,  approval, order or authorization of, or registration,
qualification, designation, declaration or filing with, any person (governmental
or  private)  on the  part of the  Company  or its  Subsidiary  is  required  in
connection  with  the  consummation  of the  transactions  contemplated  by this
Agreement and the Ancillary Documents.

                  2.6  Litigation.  Except as set forth in the SEC Documents (as
defined below),  there is no civil,  criminal or  administrative  action,  suit,
claim, notice, hearing, inquiry, proceeding or investigation at law or in equity
by  or  before   any  court,   arbitrator   or   similar   panel,   governmental
instrumentality  or other  agency now pending or, to the best  knowledge  of the
Company,  threatened  against  the  Company  or its  Subsidiary  or any of their
respective  directors or executive officers in their capacities as directors and
executive  officers of the  Company or the assets  (including  the  Intellectual
Property) of the Company or its Subsidiary (a "Litigation"). Neither the Company
nor its Subsidiary is a party or subject to the  provisions of any order,  writ,
injunction,   judgment  or  decree  of  any  court  or   government   agency  or
instrumentality.  There is no action,  suit,  proceeding or investigation by the
Company or its  Subsidiary  currently  pending or which either of the Company or
its Subsidiary intends to initiate.
<PAGE>
                  2.7 Compliance with Other  Instruments.  The Company is not in
violation or default of any  provisions  (a) of its Second  Amended and Restated
Certificate of Incorporation,  as amended, or Amended and Restated Bylaws or (b)
of any instrument,  judgment,  order,  writ, decree or contract to which it is a
party or by which it is bound,  or to its best  knowledge,  of any  provision of
domestic (federal,  state or local) or foreign law, statute,  rule or regulation
applicable  to the  Company  except,  with  respect  to clause  (b),  where such
violation would not,  individually or in the aggregate,  have a Material Adverse
Effect.  The  execution,  delivery and  performance  of this  Agreement  and the
Ancillary  Documents  by the Company and the  consummation  of the  transactions
contemplated  hereby and thereby will not (x) result in any such violation or be
in conflict with or  constitute,  with or without the passage of time and giving
of notice,  either a default  under any such  agreement,  instrument,  judgment,
order, writ, decree or contract referred to in the previous sentence  (including
any registration rights agreements),  or (y) result in the creation of any lien,
charge or  Encumbrance  upon any assets of the Company or its  Subsidiary or the
suspension,  revocation,  impairment,  forfeiture, or nonrenewal of any material
permit,  license,  authorization,  or approval  applicable to the Company or its
Subsidiary, their business or operations or any of their assets or properties.

                  2.8 Financial Statements.  The financial statements (including
any related schedule and/or notes) included in the SEC Documents (the "Financial
Statements")  are complete  and correct in all  material  respects and have been
prepared in accordance with generally accepted accounting  principles applied on
a consistent basis throughout the periods  indicated.  The Financial  Statements
fairly  present the  consolidated  financial  condition,  operating  results and
changes in  shareholders'  equity of the  Company  as of the dates,  and for the
periods,  indicated  therein.  Except  as set  forth in the SEC  Documents,  the
Company has no liabilities or obligations,  contingent or otherwise,  except (i)
liabilities  and  obligations  in the respective  amounts  reflected or reserved
against in the Company's balance sheet (the "Balance Sheet") as of June 30, 1997
included in the SEC Documents or (ii)  liabilities and  obligations  (matured or
unmatured,  fixed or  contingent)  incurred  since June 30, 1997 in the ordinary
course of business  consistent  (in amount and kind) with past practice (none of
which is a liability  resulting  from breach of  contract,  breach of  warranty,
tort, infringement,  claim or lawsuit) which individually or in the aggregate do
not have a Material  Adverse  Effect.  Since June 30, 1997,  the Company and its
Subsidiary  have operated their  business only in the ordinary  course and there
has not been  individually  or in the  aggregate  any  change  that would have a
Material  Adverse  Effect (a  "Material  Adverse  Change")  other  than  changes
disclosed in the SEC  Documents  or otherwise  set forth in Schedule 2.8 hereto.
Except as set forth in the SEC Documents, the Company has never had, nor does it
presently have, any  subsidiaries,  nor has it owned, nor does it presently own,
whether  directly or indirectly  owned,  any capital stock or other  proprietary
interest,  directly  or  indirectly,  in any  corporation,  association,  trust,
partnership, joint venture or other entity.

                  2.9 SEC Filings.  The Company has filed all proxy  statements,
reports  and other  documents  required  to be filed by it under the  Securities
Exchange Act of 1934,  as amended (the  "Exchange  Act") from and after July 20,
1995 (the "SEC Documents"), and the Company has delivered to the Investor:

         (a) its quarterly  report on Form 10-Q for the quarter  ended  December
             31, 1996;

         (b) its  quarterly  report on Form 10-Q for the quarter ended March 31,
             1997;
<PAGE>
         (c) its  quarterly  report on Form 10-Q for the quarter  ended June 30,
             1997;

         (d) its annual report on Form 10-K for the fiscal year ended
             September 30, 1996; and

         (e) its  proxy  statement  to  stockholders  as  filed  with the SEC on
             January 8, 1997.

                  Each SEC Document was in compliance in all materials  respects
with the requirements of its respective  report form and, as of its filing date,
no such SEC  Document  filed by the Company  with the  Securities  and  Exchange
Commission  ("SEC") contained any untrue statement of a material fact or omitted
to state any material fact  required to be stated  therein or necessary in order
to make the statements  made therein,  in the light of the  circumstances  under
which they were made, not misleading.

                  2.10 Other  Information.  The  Company has  delivered  to each
Investor  copies  of all  press  releases,  reports  to  stockholders  and other
documents released to the public since October 1, 1996.

                  2.11. Intellectual Property Rights. (a) Except as disclosed on
Schedule 2.11(a) hereto,  the Company or its Subsidiary owns or has the right to
use all of the Intellectual  Property (as defined below) necessary,  required or
desirable for the conduct of its business as presently or as presently  proposed
to be conducted,  except where the absence of any thereof would not individually
or in the aggregate have a Material Adverse Effect.

                  (b)  Except as  disclosed  on  Schedule  2.11(b),  to the best
knowledge of the Company, the Company has not interfered with, infringed upon or
misappropriated  any Intellectual  Property rights of third parties,  except for
interferences,  infringements and misappropriations which would not individually
or in the  aggregate  have a Material  Adverse  Effect,  and the Company has not
received  any  claim,   demand  or  notice   alleging  any  such   interference,
infringement  or  misappropriation  (including any claim that it must license or
refrain from using any Intellectual  Property rights of any third party). To the
best  knowledge of the Company,  no third party has interfered  with,  infringed
upon or misappropriated any Intellectual Property rights of the Company,  except
for  interferences,   infringements  and   misappropriations   which  would  not
individually or in the aggregate have a Material Adverse Effect.

                  As used in this Agreement,  "Intellectual  Property" means all
intellectual  property owned, leased,  licensed,  and used by the Company or its
Subsidiary,  including  without  limitation,  (i) all world wide  inventions and
discoveries  (whether  patentable or unpatentable  and whether or not reduced to
practice),  all improvements  thereto, and all patents,  patent applications and
patent    disclosures,    together   with   all   reissuances,    continuations,
continuations-in-part,  revisions,  extensions and reexaminations  thereof, (ii)
all trademarks,  service marks,  trade dress,  logos,  trade names and corporate
names, together with all translations, adaptations, derivations and combinations
thereof and including all goodwill associated  therewith,  and all applications,
registrations,  renewals and  derivatives  in  connection  therewith,  (iii) all
copyrightable  works,  all copyrights and all  applications,  registrations  and
renewals  in  connection  therewith,  (iv) all mask works and all  applications,
registrations  and renewals in connection  therewith,  (v) all  know-how,  trade
secrets  and   confidential   business   information,   whether   patentable  or
unpatentable and whether or not reduced to practice  (including ideas,  research
<PAGE>
and development, know-how, formulas, compositions,  manufacturing and production
processes and techniques,  technical data,  designs,  drawings,  specifications,
customer  and  supplier  lists,  addresses,  phone  numbers,  pricing  and  cost
information,  and business and marketing  plans and  proposals),  (vi) all other
proprietary  rights of any type of  description  (regardless of whether the same
have been  formally  registered),  (vii) all  copies  and  tangible  embodiments
thereof (in whatever  form or medium) and (viii) all licenses and  agreements in
connection with the foregoing.

                  2.12.  Title to  Assets  and  Properties;  Insurance.  (a) The
Company  has good and  marketable  title,  or a valid  leasehold  interest in or
contractual  right to use, all of its assets and  properties,  free and clear of
any mortgages,  judgments, claims, liens, security interests,  pledges, escrows,
charges   or   other   encumbrances   of  any  kind  or   character   whatsoever
("Encumbrances"),  except in each case for such  defects in title and such other
liens and Encumbrances which do not individually or in the aggregate  materially
detract  from the  value to the  Company  of the  properties  and  assets of the
Company and its Subsidiary taken as a whole.

                  (b) The Company and its Subsidiary  maintain insurance in such
amounts   (to  the   extent   available   in  the  public   market),   including
self-insurance,  retainage and deductible arrangements,  and of such a character
as is reasonable for companies engaged in the same or similar business.

                  2.13. Compliance with Laws; Permits. (a) Except as provided in
Schedule  2.13,  the  Company  and its  Subsidiary  are in  compliance,  and the
business of the Company and its  Subsidiary  have been  conducted in  compliance
with, all federal,  state,  local and foreign laws,  rules,  ordinances,  codes,
consents,  authorizations,   registrations,  regulations,  decrees,  directives,
judgments  and orders  applicable to them,  their  business and the ownership of
their  assets  including,  but not  limited to,  Environmental  Laws (as defined
below)  except  where the  failure to comply  would not  individually  or in the
aggregate have a Material  Adverse  Effect.  The Company and its Subsidiary have
all  federal,   state,  local  and  foreign  governmental   licenses,   permits,
qualifications  and authorizations  ("Permits")  necessary in the conduct of the
business as currently conducted.  All such Permits are in full force and effect,
and no  violations  have  been  recorded  in  respect  of any such  Permits;  no
proceeding  is pending or, to the best  knowledge of the Company,  threatened to
revoke or limit any such Permit; and no such Permit will be suspended,  canceled
or  adversely  modified  as a  result  of the  execution  and  delivery  of this
Agreement or the Ancillary  Documents and the  consummation of the  transactions
contemplated  hereby or  thereby,  except in any of the  foregoing  cases  where
failure to have such Permit would not  individually  or in the aggregate  have a
Material Adverse Effect.

                           (b) For  purposes of this  Agreement,  "Environmental
Laws" means,  without  limitation,  the  Comprehensive  Environmental  Response,
Compensation  and Liability Act, 42 U.S.C.  ss.ss.  9601, et seq.; the Emergency
Planning and Community  Right-to-Know  Act of 1986, 42 U.S.C.  ss.ss.  11001, et
seq.;  the Resource  Conservation  and Recovery Act, 42 U.S.C.  ss.ss.  6901, et
seq.;  the Toxic  Substances  Control Act, 15 U.S.C.  ss.ss.  2601, et seq.; the
Federal  Insecticide,  Fungicide,  and Rodenticide Act, 7 U.S.C.  ss.ss. 136, et
seq.;  the Clean Air Act, 42 U.S.C.  ss.ss.  7401, et seq.;  the Clean Water Act
(Federal Water Pollution Control Act), 33 U.S.C.  ss.ss. 1251, et seq.; the Safe
Drinking Water Act, 42 U.S.C.  ss.ss. 300f, et seq.; the Occupational Safety and
Health  Act,  29  U.S.C.   ss.ss.   641,  et  seq.;   the  Hazardous   Materials
<PAGE>
Transportation Act, 49 U.S.C. ss.ss. 1801, et seq.; as any of the above statutes
have  been or may be  amended  from  time to time,  all  rules  and  regulations
promulgated  pursuant  to any of the  above  statutes,  and any  other  foreign,
federal,  state or local law, statute,  ordinance,  rule or regulation governing
environmental  matters,  as the same  have been or may be  amended  from time to
time,  including  any common law cause of action  providing  any right or remedy
with  respect  to  environmental   matters,  and  all  applicable  judicial  and
administrative decisions, orders, and decrees relating to environmental matters.

                  2.14.  Offering  Exemption.   Assuming  the  accuracy  of  the
representations and warranties contained in Section 3 hereof, the offer and sale
of the Common  Stock and the  issuance  and  delivery of the Common Stock to the
Investors are each exempt from registration under the Securities Act of 1933, as
amended (the  "Securities  Act") and under applicable state securities and "blue
sky"  laws,  as  currently  in  effect  and are  otherwise  in  compliance  with
applicable federal and state securities laws.

                  2.15.  Taxes.  The  Company and its  Subsidiary  have filed or
caused to be filed all income tax  returns  which are  required  to be filed and
have paid or caused to be paid all Taxes (as  defined  below)  that have  become
due,  except  Taxes the  validity or amount of which is being  contested in good
faith by appropriate  proceedings  and with respect to which  adequate  reserves
have been set aside.  "Taxes," for purposes of this Agreement,  means any taxes,
assessments, duties, fees, levies, imposts, deductions, withholdings, including,
without limitation,  income,  gross receipts,  ad valorem,  value added, excise,
real or personal property,  asset,  sales, use, license,  payroll,  transaction,
capital,   net  worth  and  franchise  taxes,   estimated  taxes,   withholding,
employment,   social  security,   workers  compensation,   utility,   severance,
production,  unemployment compensation,  occupation,  premium, windfall profits,
transfer and gains taxes, or other governmental charges of any nature whatsoever
imposed by any  government  or taxing  authority  of any  country  or  political
subdivision of any country and any liabilities with respect  thereto,  including
any  penalties,  additions to tax, fines or interest  thereon,  and includes any
liability  of the  Company  and its  Subsidiary  arising  under any tax  sharing
agreement to which it is or has been a party.

                  3.  Representations  and  Warranties  of  the  Investor.  Each
Investor, severally and not jointly, hereby represents and warrants that:

                  3.1  Authorization.  This Agreement  constitutes its valid and
legally binding obligation, enforceable in accordance with its terms.

                  3.2 Purchase Entirely for Own Account.  This Agreement is made
with each  Investor  in  reliance  upon each  Investor's  representation  to the
Company,  which by such  Investor's  execution of this  Agreement  such Investor
hereby  confirms,  that the Common Stock to be received by such Investor will be
acquired for  investment for such  Investor's  own account,  not as a nominee or
agent,  for  investment  purposes  only,  and not with a view to the  resale  or
distribution  of any part thereof within the meaning of the Securities  Act, and
that  such  Investor  has  no  present   intention  of  selling,   granting  any
participation  in,  or  otherwise  distributing  the  same.  By  executing  this
Agreement,  each Investor further represents that it does not have any contract,
undertaking, agreement or arrangement with any person to sell, transfer or grant
participation to such person or to any third person,  with respect to the Common
Stock. Each Investor represents that it will not, directly or indirectly, offer,
sell,  pledge,  transfer or otherwise  dispose of (or solicit any offers to buy,
<PAGE>
purchase or  otherwise  acquire or take a pledge of) any of the shares of Common
Stock except in  compliance  with the  Securities  Act of 1933,  as amended (the
"Act"),  and the rules and  regulations  promulgated  thereunder  and applicable
state  securities  laws.  Each  Investor  represents  that it has full power and
authority to enter into this Agreement.

                  3.3 Disclosure of Information.  Each Investor  believes it has
received all the information it considers  necessary or appropriate for deciding
whether to purchase the Common Stock.  Each Investor further  represents that it
has had an  opportunity  to ask questions  and receive  answers from the Company
regarding  the terms and  conditions  of the offering of the Common  Stock.  The
foregoing,  however, does not limit or modify the representations and warranties
of the Company in Section 2 of this  Agreement or the right of each  Investor to
rely thereon.

                  3.4  Investment  Experience.  Each  Investor is an investor in
securities of companies in the  development  stage and  acknowledges  that it is
able to fend for itself,  can bear the economic risk of its  investment  and has
such knowledge and  experience in financial or business  matters such that it is
capable  of  evaluating  the merits  and risks of its  investment  in the Common
Stock.

                  3.5  Accredited  Investor.  Each  Investor  is an  "accredited
investor"  within the meaning of SEC Rule 501 of  Regulation  D, as presently in
effect.  Each Investor has  completed or caused to be completed the  Certificate
for Investors  attached  hereto as Exhibit B-1 or B-2, as  appropriate,  and the
responses provided therein shall be true as of the Closing.

                  3.6 Restricted Securities.  Each Investor understands that the
shares  of  Common  Stock it is  purchasing  are  characterized  as  "restricted
securities" ("Restricted Securities") under the federal securities laws inasmuch
as they are being  acquired  from the Company in a  transaction  not involving a
public  offering  and that  under  such  laws and  applicable  regulations  such
securities  may not be resold  without  registration  under  the Act,  except in
certain limited circumstances. In this connection, each Investor represents that
it is familiar with SEC Rule 144, as presently in effect,  and  understands  the
resale limitations imposed thereby and by the Act.

                  4.  Certain Covenants

                  4.1 Use of Proceeds.  The net proceeds received by the Company
from the sale of the Common Stock as contemplated by this Agreement will be used
by the Company for general working capital purposes.

                  4.2 Rule 144 Reporting. With a view to making available to the
Investors  the benefits of certain  rules and  regulations  of the SEC which may
permit the sale of the  Common  Stock to the public  without  registration,  the
Company agrees to use its best efforts to:

                           (a) make and keep public  information  available,  as
         those terms are understood and defined in rule 144 under the Securities
         Act, at all times;

                           (b) use its best  efforts  to file  with the SEC in a
         timely manner all reports and other  documents  required of the Company
         under the Securities Act and the Exchange Act; and
<PAGE>
                           (c) so  long  as the  Investor  owns  any  Restricted
         Securities (as defined in Section 3.6 hereof),  furnish to the Investor
         forthwith  upon  request a written  statement  by the Company as to its
         compliance  with the  reporting  requirements  of Rule 144,  and of the
         Securities  Act and the Exchange  Act, a copy of the most recent annual
         or  quarterly  report of the  Company  filed  with the  Securities  and
         Exchange  Commission,  and such  other  reports  and  documents  of the
         Company  and  other  information  in the  possession  of or  reasonably
         obtainable  by the Company as the  Investor may  reasonably  request in
         availing  itself  of any  rule or  regulation  of the SEC  allowing  an
         Investor to sell any such securities without registration.

                  5. Transfer  Taxes.  The Company  agrees that it will pay, and
will hold each Investor harmless from, any and all liability with respect to any
stamp or similar Taxes which may be determined to be payable in connection  with
the execution and delivery and performance of this  Agreement,  and that it will
similarly pay and hold each  Investor  harmless from all Taxes in respect of the
issuance of the Common Stock to such Investor.

                  6.  Expenses.  (a)  Except as set forth in Section  6(b),  the
Company and each Investor shall pay all the costs and expenses incurred by it or
on its behalf in  connection  with this  Agreement and the  consummation  of the
transactions contemplated hereby.

                           (b)  Within  10 days  from the  receipt  of a billing
         statement  from one of the Pequot  entities  listed on  Schedule 1 (the
         "Pequot  Entities"),  the  Company  shall pay and shall  reimburse  the
         Pequot  Entities for all of their  reasonable  legal costs and expenses
         incurred in connection with this transaction (including the negotiation
         and  preparation of this Agreement and the Ancillary  Documents and the
         consummation  of the  transactions  contemplated  hereby and  thereby);
         provided, however, in no event shall the liability of the Company under
         this Section 6(b) in the aggregate exceed $25,000.

                  7.   Indemnification.

                  7.1  General  Indemnification.  The Company  shall  indemnify,
defend  and hold each  Investor,  its  affiliates,  their  respective  officers,
directors, partners, employees, agents, representatives,  successors and assigns
(each an  "Investor  Entity")  harmless  from and against all Losses (as defined
below) incurred or suffered by an Investor Entity (whether  incurred or suffered
directly  or  indirectly  through  ownership  of capital  stock of the  Company)
arising from the breach of any of the representations,  warranties, covenants or
agreements  made by the Company in this Agreement or in any Ancillary  Document.
Each Investor,  severally and not jointly, shall indemnify,  defend and hold the
Company,  its  affiliates,  their  respective  officers,  directors,  employees,
agents,  representatives,  successors  and assigns  harmless  against all Losses
arising from the breach of any of its representations,  warranties, covenants or
agreements  in this  Agreement or in any  Ancillary  Documents.  Notwithstanding
anything to the contrary in this Agreement,  no  indemnification  payment by the
Company pursuant to this Section 7 with respect to any Losses otherwise  payable
hereunder as a result of a breach of the  representations  and warranties of the
Company (other than any Losses resulting from breaches of the representation and
warranty in Section 2.3 which shall not be subject to the Deductible (as defined
below)) shall be payable  until the time as such Losses shall  aggregate for all
Investor Entities to more than $75,000 (the "Deductible"),  and then only to the
extent that such Losses, in the aggregate for all Investor Entities,  exceed the
Deductible.
<PAGE>
                  7.2 Indemnification  Principles.  For purposes of this Section
7, (i) "Losses" shall mean each and all of the following items: claims,  losses,
(including,  without limitation,  losses of earnings) liabilities,  obligations,
payments,  damages,  charges,  judgments,  fines,  penalties,  amounts  paid  in
settlement,  costs and expenses (including,  without limitation,  interest which
may be imposed in connection therewith, costs and expenses of investigation,
actions,  suits,  proceedings,  demands,  assessments  and  fees,  expenses  and
disbursements of counsel,  consultants and other experts);  and (ii) each of the
representations  and  warranties  made by any party in this Agreement and in the
Ancillary  Documents  shall be deemed to have been made without the inclusion of
limitations or  qualifications  as to  materiality,  such as the words "Material
Adverse  Effect,"  "immaterial,"  "material"  and "in all material  respects" or
words of similar  import.  Any payment (or deemed  payment) by the Company to an
Investor  pursuant to this  Section 7, shall be treated  for federal  income tax
purposes  as an  adjustment  to the price paid by such  Investor  for the Common
Stock pursuant to this Agreement.

                  7.3 Claim Notice. A party seeking  indemnification  under this
Section 7 shall,  promptly upon becoming  aware of the facts  indicating  that a
claim  for  indemnification  may be  warranted,  give  to the  party  from  whom
indemnification  is being sought a claim notice  relating to such Loss (a "Claim
Notice").  Each  Claim  Notice  shall  specify  the  nature  of the  claim,  the
applicable  provision(s) of this Agreement or other  instrument  under which the
claim for indemnity arises, and, if possible, the amount or the estimated amount
thereof.  No failure  or delay in giving a Claim  Notice (so long as the same is
given prior to expiration of the representation or warranty upon which the claim
is based) and no failure to include  any  specific  information  relating to the
claim (such as the amount or estimated  amount  thereof) or any reference to any
provision  of this  Agreement or other  instrument  under which the claim arises
shall affect the obligation of the party from whom indemnity is sought.

                  8. Remedies.  In case any one or more of the covenants  and/or
agreements  set forth in this  Agreement  shall have been  breached by any party
hereto, each Investor, with respect to a breach by the Company, and the Company,
with respect to a breach by an Investor,  may proceed to protect and enforce its
rights  either by suit in equity  and/or  by action at law,  including,  but not
limited  to, an action  for  damages  as a result of any such  breach  and/or an
action for specific  performance of any such covenant or agreement  contained in
this Agreement.

                  9. Miscellaneous. 


                  9.1 Survival of Warranties.  The  warranties,  representations
and covenants of the Company and each Investor  contained in or made pursuant to
this  Agreement  shall survive the execution and delivery of this  Agreement and
the Closing and shall in no way be affected by any  investigation of the subject
matter thereof made by or on behalf of the Investors or the Company.

                  9.2  Successors  and  Assigns.  Except as  otherwise  provided
herein, the terms and conditions of this Agreement shall inure to the benefit of
and be binding upon the  respective  successors,  permitted  assigns,  heirs and
personal  representatives of the parties (including transferees of any shares of
Common Stock sold hereunder),  except that the Company may not assign its rights
and  obligations  under this  Agreement to any person  without the prior written
consent of the  Investors  purchasing  two-thirds of the Common Stock to be sold
pursuant to this Agreement, except in connection with a merger, consolidation or
<PAGE>
sale of all or substantially  all of the assets of the Company.  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.

                  9.3  Governing  Law. This  Agreement  shall be governed by and
construed  under  the  laws of the  State  of New  York  without  regard  to the
principles  of conflicts  or choice of law.  Each of the parties  hereto  hereby
irrevocably and unconditionally consents to submit to the exclusive jurisdiction
of the courts of the State of New York and of the United States of America,  for
any  Litigation  arising out of or relating to this  Agreement and the Ancillary
Documents  and the  transactions  contemplated  hereby and thereby,  and further
agrees  that  service  of any  process,  summons,  notice  or  document  by U.S.
registered  mail to its respective  address set forth in this Agreement shall be
effective  service of process for any Litigation  brought against it in any such
court.

                  9.4  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.

                  9.5 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.

                  9.6 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 on the signature page hereof in the case of the Company
and on Schedule 1 in the case of each Investor, or at such other address as such
party  may  designate  by ten (10)  days'  advance  written  notice to the other
parties.

                  9.7 Finder's Fee. Each party represents that it neither is nor
will be obligated for any finders' fee or  commission  in  connection  with this
transaction.  Each Investor agrees to indemnify and to hold harmless the Company
from any  liability  for any  commission  or  compensation  in the  nature  of a
finders' fee (and the costs and expenses of defending  against such liability or
asserted  liability)  for which such Investor or any of its officers,  partners,
employees, or representatives is responsible.

                  The  Company   agrees  to  indemnify  and  hold  harmless  the
Investors from any liability for any commission or compensation in the nature of
a finders' fee (and the costs and expenses of defending  against such  liability
or asserted  liability) for which the Company or any of its officers,  employees
or representatives is responsible.

                  9.8  Attorneys'  Fees.  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.
<PAGE>
                  9.9 Amendments  and Waivers.  No term of this Agreement may be
amended,  discharged  or  terminated  and  the  observance  of any  term of this
Agreement may not be waived  (either  generally or in a particular  instance and
either retroactively or prospectively), without the prior written consent of the
Investors purchasing  two-thirds of the Common Stock to be sold pursuant to this
Agreement.  Any amendment or waiver  effected in accordance  with this paragraph
shall be  binding  upon  each  holder of any  securities  purchased  under  this
Agreement at the time  outstanding,  each future holder of all such  securities,
and the Company.  No waiver of any of the provisions of this Agreement  shall be
deemed to or shall constitute a waiver of any other provision hereof (whether or
not similar).  No delay on the part of any party in exercising any right,  power
or privilege hereunder shall operate as a waiver thereof.

                  9.10 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.

                  9.11  Entire  Agreement.  This  Agreement  and  the  documents
referred  to herein  constitute  the entire  agreement  among the parties and no
party  shall be  liable  or  bound  to any  other  party  in any  manner  by any
warranties,  representations,  or  covenants  except as  specifically  set forth
herein or therein.

                  9.12 Press  Releases  and  Announcements.  Each of the parties
hereto agrees that it will not issue any press release or announcement  relating
to the subject  matter of this Agreement  without the prior written  approval of
the  other  parties;  provided,  however,  that any  party  may make any  public
disclosure it believes in good faith is required by law or regulation  (in which
case the disclosing  party shall advise the other  parties,  provide them with a
copy  of the  proposed  disclosure  prior  to  making  the  disclosure,  and use
reasonable efforts to agree upon the text of such press release,  before issuing
any such press release).

                [Remainder of this page intentionally left blank]

                                                        

<PAGE>



                  IN WITNESS  WHEREOF,  the parties  have  executed  this Common
Stock Purchase 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




                         COMMON STOCK PURCHASE 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









                         COMMON STOCK PURCHASE 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.































                         COMMON STOCK PURCHASE 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

































                         COMMON STOCK PURCHASE AGREEMENT


<PAGE>



                                  TERENCE D. WALL


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









































                         COMMON STOCK PURCHASE AGREEMENT