BY-LAWS

                                       OF

                              DIANON SYSTEMS, INC.
                            (A DELAWARE CORPORATION)

                                    ARTICLE I

                                  STOCKHOLDERS

         Section 1.01 ANNUAL  MEETING.  The annual meeting of the  stockholders,
for the purpose of electing directors and transacting such other business as may
come  before it,  shall be held on such date and at such time and place,  either
within or without the State of  Delaware,  as may be  specified  by the Board of
Directors.

         Section 1.02 SPECIAL MEETINGS. Special meetings of the stockholders may
be called only by the  Chairman of the Board,  the  President or by the Board of
Directors.  At a special  meeting  of the  stockholders,  no  business  shall be
transacted  which is not related to the purpose or purposes stated in the notice
of meeting.

         Any special meeting of the stockholders  shall be held on such date and
at such time and place,  either within or without the State of Delaware,  as may
be specified  by the person or persons  calling the meeting in the notice of the
meeting.

         Section 1.03 NOTICE OF MEETINGS.  Written notice of each  stockholders'
meeting,  stating the place,  date and hour of the meeting  and,  the purpose or
purposes  thereof,  shall be given to each  stockholder  entitled to vote at the
meeting  not less  than ten nor more  than  sixty  days  before  the date of the
meeting. Any previously scheduled meeting of the stockholders may be canceled by




resolution of the Board of Directors  upon public notice given prior to the date
previously scheduled for such meeting.

         Section 1.04 QUORUM;  ADJOURNMENT.  Except as otherwise provided in the
Restated  Certificate of Incorporation or required by law, at any meeting of the
stockholders  a majority of the shares  entitled  to vote,  present in person or
represented by proxy,  shall constitute a quorum.

         The  Chairman of the meeting or the vote of a majority of the shares so
represented  may adjourn the meeting from time to time,  whether or not there is
such a quorum.  No notice of the time and place of  adjourned  meetings  need be
given except as required by law.

         Section 1.05 CONDUCT OF MEETINGS.  The chief  executive  officer  shall
preside at any meeting of the stockholders. In such person's absence, such other
person as shall have been designated by the chief executive officer or the Board
of Directors  shall  preside.  The order of business at any meeting  shall be as
determined by such Presiding Officer. 

         The  presiding  officer  shall have the power to prescribe  such rules,
regulations  and  procedures and to do all such things as in his judgment may be
necessary or desirable for the proper conduct of the meeting, including, without
limitation,  the  establishment  of procedures for the  maintenance of order and
safety, limitations on the time allotted to questions or comments,  restrictions
on entry to the meeting after the time  scheduled for the  commencement  thereof
and the opening and closing of the voting polls.

         If present,  the Secretary shall act as secretary of any meeting of the
stockholders.  In the  Secretary's  absence,  such other person as the presiding
officer shall designate  shall act as secretary of the meeting.  





         It shall be the duty of the Secretary to prepare and make, at least ten
days  before  every  meeting  of  the  stockholders,  a  complete  list  of  the
stockholders entitled to vote at the meeting, arranged in alphabetical order and
showing the address of each  stockholder and the number of shares  registered in
the name of each stockholder.  Such list shall be open to the examination of any
stockholder,  for any purpose germane to the meeting,  during ordinary  business
hours, for a period of at least ten days prior to the meeting, either at a place
within the city where the meeting is to be held,  which place shall be specified
in the notice of the meeting,  or, if not so  specified,  at the place where the
meeting is to be held.  The list shall also be produced and kept at the time and
place of the meeting during the whole time thereof,  and may be inspected by any
stockholder who is present.

         Section  1.06  VOTING.   Except  as  otherwise   provided  in  Restated
Certificate  of  Incorporation  or required by law,  (i) every holder of capital
stock  which is entitled to vote shall be entitled to one vote for each share of
such stock registered in the name of such  stockholder,  (ii) directors shall be
elected by a plurality  of the votes  validly cast at the meeting by the holders
of shares  entitled to vote for the  election of  directors  and (iii) any other
corporate action shall be authorized if, with respect to shares entitled to vote
on the action,  the votes  validly cast in favor of the action  exceed the votes
validly cast in  opposition  to the action.

         Section  1.07  RECORD  DATE.  For  the  purpose  of   determining   the
stockholders entitled to notice of or to vote at any meeting of the stockholders
or any  adjournment  thereof,  or entitled to receive payment of any dividend or
other  distribution  or  allotment  of any rights,  or entitled to exercise  any
rights in respect of any  change,  conversion  or  exchange  of stock or for the
purpose of any other lawful action,  the Board of Directors may fix, in advance,




a record date,  which shall not be more than sixty nor less than ten days before
the date of such  meeting,  nor more than sixty days prior to any other  action.


         Section 1.08. NOMINATION OF DIRECTORS. Subject to the rights of holders
of any outstanding preferred stock, only persons who are nominated in accordance
with the following procedures shall be eligible for election as directors of the
Corporation.  Nominations  for  election of  directors  may be made at an annual
meeting of  stockholders  either by the Board of Directors or by any stockholder
who is a  stockholder  on the date of the giving of the notice  provided  for in
this Section 1.08 and on the record date for the  determination  of stockholders
entitled to vote at such annual  meeting.  An eligible  stockholder may nominate
persons for election as directors at an annual meeting of  stockholders  only if
such  stockholder  has caused proper written  notice with respect  thereto to be
delivered to, or mailed and received at, the principal  executive offices of the
Corporation  not more than 120 days nor less  than 90 days  prior to the date of
the  annual  meeting;  provided,  however,  that in the event that less than 100
days' notice or prior public  disclosure  of the date of the meeting is given to
stockholders,  such  written  notice  will also be timely if so  received by the
close of business on the 10th day  following  the first to occur of (y) the date
on which  such  notice of the date of the annual  meeting  was mailed or (z) the
date on which  public  disclosure  of such date was made.  For such notice by an
eligible stockholder to be proper, such notice shall set forth: (i) the name and
business and  residential  addresses of the  stockholder who intends to make the
nomination  and of the  person or  persons  to be  nominated;  (ii) the class or
series and number of shares of capital stock of the  Corporation  that are owned
beneficially or of record by such stockholder;  (iii) a representation that such
stockholder intends to appear in person or by proxy as a holder of record at the
meeting to  nominate  the  person or persons  specified  in the  notice;  (iv) a
description of all arrangements or  understandings  between such stockholder and




each  nominee  proposed  by the  stockholder  and any other  person  or  persons
(identifying  such  person  or  persons)  pursuant  to which the  nomination  or
nominations are to be made by the stockholder;  (v) the principal  occupation or
employment  of, and the classes or series and number of shares of capital  stock
of the  Corporation  that are owned  beneficially or of record by, the person or
persons  to be  nominated  and such other  information  regarding  each  nominee
proposed  by such  stockholder  as would be  required  to be included in a proxy
statement  filed  pursuant to the proxy  rules of the  Securities  and  Exchange
Commission;  and (vi) the consent of each  nominee to serve as a director of the
Corporation  if so  elected. 

         No  person  shall  be  eligible  for  election  as a  director  of  the
Corporation unless nominated in accordance with the procedures set forth in this
Section  1.08.  If the facts show that a nomination  was not made in  accordance
with the foregoing  provisions,  the  Presiding  Officer of the meeting shall so
determine and declare to the meeting,  whereupon the defective  nomination shall
be disregarded.  Public  disclosure of the date of a forthcoming  meeting may be
made by the Corporation for purposes of this Section 1.08 not only by the giving
of the  formal  notice  of the  meeting  but also (i) by  notice  to a  national
securities exchange or to the National  Association of Securities Dealers,  Inc.
(if the Corporation's  common stock is then listed on such exchange or quoted on
NASDAQ),  (ii) by filing a report under  Section 13 or 15(d) of the Exchange Act
(if the Corporation is then subject thereto), (iii) by a mailing to stockholders
or (iv) by general press release.  

         Section 1.09 BUSINESS AT ANNUAL MEETINGS. No business may be transacted
at an annual meeting of  stockholders  other than business that is (i) specified
in the  notice  of  meeting  (or  any  supplement  thereto)  given  by or at the
direction of the Board of Directors,  (ii) otherwise properly brought before the
annual  meeting  by or at the  direction  of the  Board  of  Directors  or (iii)





otherwise properly brought before the annual meeting by a stockholder who (w) is
a stockholder of record on the date of the giving of the notice  provided for in
this Section 1.09 and on the record date for the  determination  of stockholders
entitled  to vote at such  annual  meeting  and (x)  complies  with  the  notice
procedures  set forth in this Section  1.09. An eligible  stockholder  may bring
business  before an annual  meeting only if such  stockholder  has caused proper
written  notice with respect  thereto to be delivered to, or mailed and received
at, the principal  executive  offices of the  Corporation not more than 120 days
nor  less  than 90 days  prior  to the  date of the  annual  meeting;  provided,
however,  that in the event  that less  than 100  days'  notice or prior  public
disclosure  of the date of the meeting is given to  stockholders,  such  written
notice  will also be timely if so  received by the close of business on the 10th
day  following  the first to occur of (y) the date on which  such  notice of the
date of the annual meeting was mailed or (z) the date on which public disclosure
of such date was made. For such notice by an eligible  stockholder to be proper,
such notice must set forth as to each matter such stockholder  proposes to bring
before the annual meeting: (1) a brief description of the business desired to be
brought before the meeting and the reasons for  conducting  such business at the
meeting;  (2) the name and record  address  of the  stockholder  who  intends to
propose such  business;  (3) the class or series and number of shares of capital
stock of the  Corporation  that are  owned  beneficially  or of  record  by such
stockholder;  (4) a description of all  arrangements or  understandings  between
such  stockholder  and any other  person or persons  (including  their names) in
connection  with the  proposal  of such  business  by such  stockholder  and any
material interest of the stockholder in such business;  and (5) a representation
that such  stockholder  intends  to  appear in person or by proxy at the  annual
meeting  to bring  such  business  before  the  meeting. 




         No business  shall be conducted at the annual  meeting of  stockholders
except  business  brought  before the  annual  meeting  in  accordance  with the
procedures  set  forth in this  Section  1.09,  provided,  however,  that,  once
business has been properly  brought before the annual meeting in accordance with
such  procedures,  nothing  in this  Section  1.09  shall be deemed to  preclude
discussion by any stockholder of any such business.  If the Presiding Officer of
an annual meeting  determines that business was not properly  brought before the
annual  meeting in  accordance  with the  foregoing  procedures,  the  Presiding
Officer shall declare to the meeting that the business was not properly  brought
before the meeting and such business  shall not be  transacted. 

         Notwithstanding  the  foregoing  provisions  of this  Section  1.09,  a
stockholder  shall also comply with all applicable  requirements of the Exchange
Act and the rules and  regulations  thereunder  with  respect to the matters set
forth in this  Section  1.09.  Nothing in this  Section  1.09 shall be deemed to
affect any rights of  stockholders  to request  inclusion  of  proposals  in the
Company's proxy statement pursuant to Rule 14a-8 under the Exchange Act.


                                   ARTICLE II

                               BOARD OF DIRECTORS

         Section  2.01  NUMBER.   Except  as  otherwise   provided  in  Restated
Certificate of Incorporation,  the number of directors shall be the number fixed
from time to time by the Board.

         Section  2.02  ELECTION  AND  TERM.  At  each  annual  meeting  of  the
stockholders,  directors shall be elected to hold office until their  successors
are elected and qualified or until their earlier resignation or removal.





         Section 2.03  MEETINGS OF THE BOARD.  Regular  meetings of the Board of
Directors  shall be held at such times and places as the Board shall  determine.
Special  meetings of the Board shall be held whenever  called by the Chairman of
the Board,  the  President  or by a majority of the  directors  in office at the
time.  

         Section 2.04 NOTICE OF MEETINGS. No notice need be given of any regular
meeting of the Board of Directors or of any adjourned  meeting of the Board. Nor
need notice be given to any director who signs a written  waiver  thereof or who
attends the meeting  without  protesting  the lack of notice.  Notices  need not
state the purpose of the meeting.  

         Notice of each  special  meeting  of the  Board  shall be given to each
director either by first class mail at least three days before the meeting or by
telegram, telex, cable or like transmission, telecopy, personal written delivery
or telephone at least one day before the meeting.  Any notice given by telephone
shall be immediately  confirmed by telegram,  telex, cable or like transmission.
Notices are deemed to have been given:  by mail, when deposited in the mail with
postage prepaid; by telegram, telex, cable or like transmission,  at the time of
sending; and by personal delivery or telephone, at the time of delivery. Written
notices  shall be sent to a director at the address  designated  by him for that
purpose,  or, if none has been so  designated,  at his last known  residence  or
business address.

         Section 2.05 QUORUM AND VOTE OF DIRECTORS. Except as otherwise provided
in the Restated  Certificate of  Incorporation or required by law, a majority of
the entire Board of Directors  shall  constitute a quorum for the transaction of
business or of any specified  item of business and the vote of a majority of the
directors  present at a meeting  at the time of such  vote,  if a quorum is then
present,  shall be the act of the Board.




         Section  2.06  CONDUCT OF  MEETINGS.  The  Chairman of the Board or the
President,  if any,  shall preside at any meeting of the Board of Directors.  In
the  absence of the  Chairman of the Board or the  President,  a chairman of the
meeting shall be elected from the directors present.  If present,  the Secretary
shall act as  secretary  of any  meeting  of the  Board.  In the  absence of the
Secretary,  the  chairman  of the  meeting  may  appoint  any  person  to act as
secretary of the meeting.

         Section 2.07 RESIGNATIONS OF DIRECTORS. Any director of the Corporation
may resign at any time by giving  written notice to the Board of Directors or to
the Secretary of the Corporation. Such resignation shall take effect at the time
specified therein or, if such time is not specified  therein,  then upon receipt
thereof;  and  unless  otherwise  specified  therein,  the  acceptance  of  such
resignation shall not be necessary to make it effective. Section 2.08 REMOVAL OF
DIRECTORS. Any director or the entire Board of Directors may be removed, with or
without cause, at any time by the affirmative  vote of the holders of a majority
of the shares then entitled to vote at an election of directors.

         Section 2.09.  NEWLY CREATED  DIRECTORSHIPS  AND  VACANCIES.  Except as
otherwise provided in the Restated Certificate of Incorporation or by law, newly
created directorships  resulting from an increase in the number of directors and
vacancies  occurring in the Board of  Directors  for any reason,  including  the
removal of directors  with or without  cause,  may be filled by the  affirmative
vote of a majority of the directors then in office,  although less than a quorum
exists, or by a sole remaining director. 

         Section  2.10  COMMITTEES.  The Board of Directors  may, by  resolution
passed by a majority of the whole Board, designate one or more committees,  each
committee  to consist of one or more of the  directors of the  Corporation.





         The Board may designate one or more  directors as alternate  members of
any committee,  who may replace any absent or disqualified member at any meeting
of the committee. In the absence or disqualification of a member of a committee,
the member or members thereof present at any meeting and not  disqualified  from
voting,  whether or not constituting a quorum,  may unanimously  appoint another
member of the  Board to act at the  meeting  in the place of any such  absent or
disqualified  member. 

         Any such  committee,  to the extent  provided in the  resolution of the
Board but subject to the  limitation of Section  141(c) of the Delaware  General
Corporation Law, shall have and may exercise all the powers and authority of the
Board in the management of the business and affairs of the Corporation,  and may
authorize  the seal of the  Corporation  to be affixed  to all papers  which may
require it.

         The  provisions  of Section  2.04 for notice of  meetings  of the Board
shall apply also to meetings of committees,  unless different notice  procedures
shall be  prescribed  by the  Board.  

         Each such committee  shall serve at the pleasure of the Board. It shall
keep minutes of its meetings and report the same to the Board and shall  observe
such other procedures as are prescribed by the Board.

         Section 2.11 COMPENSATION OF DIRECTORS. Each director shall be entitled
to receive as compensation  for his services as director or committee  member or
for  attendance  at meetings of the Board of Directors or  committees,  or both,
such  amounts  (if any) as shall be fixed from time to time by the  Board.  Each
director shall be entitled to reimbursement  for reasonable  traveling  expenses
incurred by him in attending  any such meeting.  No such payment shall  preclude




any director from serving the  Corporation  in any other  capacity and receiving
compensation therefor.

         Section 2.12 TELEPHONIC MEETINGS.  Any one or more members of the Board
of Directors or any committee thereof may participate in a meeting of such Board
or  committee  by  means  of  conference  telephone  or  similar  communications
equipment  by means of which all persons  participating  in the meeting can hear
each  other,  and  participation  in a meeting  by such means  shall  constitute
presence in person at such meeting.

         Section  2.13  ACTION  BY  WRITTEN  CONSENT.  Any  action  required  or
permitted  to be taken  at any  meeting  of the  Board  of  Directors  or of any
committee  thereof may be taken without a meeting if all members of the Board or
the committee  consent  thereto in writing and the writing or writings are filed
with the minutes of proceedings of the Board or committee.


                                   ARTICLE III

                                    OFFICERS

         Section 3.01 OFFICERS.  The officers of the Corporation shall include a
Chairman of the Board,  a President,  a Treasurer  and a Secretary  and may also
include a Vice Chairman of the Board,  one or more Vice  Presidents  (who may be
further  classified by such descriptions as "executive,"  "senior" or "group" as
determined by the Board of Directors), a Controller,  Assistant Vice Presidents,
Assistant  Treasurers,  Assistant  Secretaries,  Assistant Controllers and other
officers and agents,  as the Board of Directors may deem necessary or desirable.

         Each officer  shall have such  authority  and perform  such duties,  in
addition to those specified in these By-Laws,  as may be prescribed by the Board
from time to time.  The Board may from time to time  authorize  any  officer  to




appoint and remove any other  officer or agent and to  prescribe  such  person's
authority and duties. Any person may hold at one time two or more offices.

         Section 3.02.  TERM OF OFFICE,  RESIGNATION  AND REMOVAL.  Each officer
shall hold office for the term for which  elected or  appointed  by the Board of
Directors,  and until the person's  successor  has been elected or appointed and
qualified or until his earlier resignation or removal.

         Any  officer  may  resign at any time by giving  written  notice to the
Board or to the Secretary of the Corporation. Such resignation shall take effect
at the time specified  therein or, if such time is not specified  therein,  then
upon receipt thereof;  and unless otherwise specified therein, the acceptance of
such resignation shall not be necessary to make it effective.

         Any officer  may be removed by the Board,  with or without  cause.  The
election  or  appointment  of an  officer  shall not of itself  create  contract
rights.

         Section 3.03 CHAIRMAN OF THE BOARD.  The Chairman of the Board shall be
a member of the Board of  Directors.  The Chairman of the Board shall preside at
all  meetings  of the  stockholders  and  the  Board  of  Directors  and,  if so
designated  by  the  Board,   shall  be  the  chief  executive  officer  of  the
Corporation.  

         Section 3.04  PRESIDENT.  Unless there shall be a Chairman of the Board
designated  by the Board of  Directors  as the chief  executive  officer  of the
Corporation,  the  President  shall  be  the  chief  executive  officer  of  the
Corporation.  Subject to the control of the Board of Directors  and the Chairman
of the Board (if designated  chief  executive  officer),  the President shall be
responsible  for the  day-to-day  management  of the business and affairs of the
Corporation  and shall enjoy all other powers  commonly  incident to the office.




         Section 3.05 VICE  PRESIDENTS.  Each of the Vice Presidents  shall have
such  authority and perform such duties as may be prescribed  from time to time.


         Section 3.06 TREASURER AND ASSISTANT  TREASURERS.  The Treasurer  shall
have the care and custody of all funds and securities of the  Corporation,  keep
accounts of receipts and  disbursements  and of deposit or custody of moneys and
other  valuables and enjoy all powers  commonly  incident to the office.

         In the case of the absence or  inability to act of the  Treasurer,  any
Assistant Treasurer may act in the Treasurer's place. 

         Section 3.07 SECRETARY AND ASSISTANT  SECRETARIES.  The Secretary shall
keep the minutes of the meetings of the  stockholders and the Board of Directors
and give notice of such  meetings,  have custody of the corporate seal and affix
and attest such seal to any  instrument to be executed  under seal and enjoy all
powers commonly  incident to the office. 

         In the case of the absence or  inability to act of the  Secretary,  any
Assistant Secretary may act in the Secretary's place.

         Section 3.08 CONTROLLER AND ASSISTANT CONTROLLERS. The Controller shall
have control of all books of account of the Corporation  (other than those to be
kept by the  Treasurer),  render  accounts  of the  financial  condition  of the
Corporation and enjoy all powers commonly incident to the office. 

         In the absence or inability  to act of the  Controller,  any  Assistant
Controller may act in the Controller's place.

         Section  3.09  COMPENSATION.   Compensation  of  officers,  agents  and
employees of the  Corporation  shall be fixed from time to time by, or under the
authority of, the Board of Directors.




                                   ARTICLE IV

                                  CAPITAL STOCK

         Section  4.01  FORM  OF  CERTIFICATES.  Unless  otherwise  provided  by
resolution  of the Board of  Directors,  the shares of stock of the  Corporation
shall  be  represented  by  certificates  which  shall  be in  such  form  as is
prescribed by law and approved by the Board.

         Section  4.02  TRANSFER OF SHARES.  Transfers of shares of stock of the
Corporation  shall be registered on its records  maintained for such purpose (i)
upon  surrender  to the  Corporation  or a transfer  agent of a  certificate  or
certificates  representing the shares  requested to be transferred,  with proper
endorsement on the  certificate or  certificates  or on a separate  accompanying
document,  together  with such  evidence of the  payment of  transfer  taxes and
compliance with other provisions of law as the Corporation or its transfer agent
may  require  or (ii)  if  shares  are not  represented  by  certificates,  upon
compliance  with such  transfer  procedures  as may be  approved by the Board or
prescribed by applicable law.

         The Corporation  shall be entitled to treat the holder of record of any
share as the  holder in fact  thereof  and,  accordingly,  shall not be bound to
recognize  any equitable or other claim to or interest in such share on the part
of any  other  person  whether  or not it shall  have  express  or other  notice
thereof,  except as expressly  provided by law.

         Section 4.03  REGULATIONS.  The Board of Directors shall have authority
to make such  rules and  regulations  as it may deem  expedient  concerning  the
issue,  transfer  and  registration  of  shares  of  stock  of the  Corporation,
including  without  limitation  such  rules  and  regulations  as may be  deemed
expedient  concerning the issue of certificates in lieu of certificates  claimed
to have been lost, destroyed, stolen or mutilated.




                                    ARTICLE V

                               GENERAL PROVISIONS

         Section  5.01  CORPORATE  SEAL.  The  Board of  Directors  may  adopt a
corporate seal, alter such seal at its pleasure,  and authorize it to be used by
causing it or a facsimile to be affixed or impressed or  reproduced in any other
manner.

         Section 5.02 VOTING UPON STOCKS.  Unless otherwise ordered by the Board
of  Directors,  the chief  executive  officer of the  Corporation,  or any other
officer of the  Corporation  designated  by the chief  executive  officer of the
Corporation, shall have full power and authority on behalf of the Corporation to
attend  and to act and to vote in  person  or by  proxy  at any  meeting  of the
holders of securities of any  corporation  in which the  Corporation  may own or
hold stock or other  securities,  and at any such meeting  shall possess and may
exercise  in  person  or by proxy  any and all  rights,  powers  and  privileges
incident  to  the  ownership  of  such  stock  or  other  securities  which  the
Corporation,  as the owner or holder thereof, might have possessed and exercised
if present. The chief executive officer of the Corporation, or any other officer
of the Corporation designated by the chief executive officer of the Corporation,
may also  execute and deliver on behalf of the  Corporation  powers of attorney,
consents,  proxies,  waivers of notice  and other  instruments  relating  to the
stocks or securities  owned or held by the  Corporation.  The Board of Directors
may, from time to time,  by resolution  confer like powers upon any other person
or persons.

         Section 5.03 AMENDMENTS. These By-Laws and any amendments hereof may be
altered,  amended,  or repealed,  and new By-Laws may be adopted, as provided in
the Restated Certificate of Incorporation.