ARTICLES OF INCORPORATION
                                       OF
                       DIAGNOSTIC REFERENCE SERVICES, INC.


         FIRST: The undersigned, DAVID B. RUDOW, whose post office address is
600 Mercantile Bank & Trust Bldg., 2 Hopkins Plaza, Baltimore, Maryland 21201, a
resident of the State of Maryland, over eighteen (18) years of age, does hereby
constitute himself an incorporator with the purpose of forming a corporation
under and by virtue of the General Laws of the State of Maryland.

         SECOND: The name of the corporation (which is hereinafter called the
"Corporation") is

                 "DIAGNOSTIC REFERENCE SERVICES, INC."

         THIRD:  The purposes for which the Corporation is formed are as 
follows:

                 (a)   To engage in the business of operating a medical
                       laboratory or laboratories and to engage generally in the
                       business of the operation of medical laboratories.

                 (b)   To acquire by purchase or otherwise, own, hold, buy,
                       sell, convey, lease, mortgage, or encumber real estate or
                       other property, personal or mixed.

                 (c)   To take, own, yield income, mortgage or otherwise give
                       liens against, and to lease, sell, exchange, transfer or
                       in any manner whatsoever to dispose of real property
                       within or without the State of Maryland wherever situate.

                 (d)   To purchase, acquire, hold, improve, sell, convey,
                       assign, release, mortgage, encumber, lease, hire and deal
                       in real and personal property of every name and nature,
                       including stocks and securities of other corporations,
                       and to loan money and take securities for the payments of
                       all sums due the





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                       Corporation, and to sell, assign and release such
                       securities.

                 (e)   To purchase, acquire, apply for, register, secure, hold,
                       own, sell, or otherwise obtain and dispose of any and all
                       copyrights, trade names and distinctive marks.

                 (f)   To carry on any other business in connection with the
                       foregoing, whether owning, operating and managing real
                       estate or otherwise.

                 (g)   To borrow money, make and issue bonds payable to bearer
                       or otherwise, and to secure the same by mortgage, deed of
                       trust or otherwise, to sell or pledge any and all
                       securities or evidence of debt owned by the Corporation,
                       and to carry on such business and to deal with the
                       property by law as may seem to be calculated, directly or
                       indirectly, to promote the objects or purposes.

                 (h)   To acquire by purchase, lease or otherwise, the property,
                       rights, business good will, franchises and assets of
                       every kind of any corporation, association, firm or
                       individual, in whole or in part, and to operate the same,
                       and to undertake, guarantee, assume the indebtedness and
                       liabilities thereof, and to pay for any property, rights,
                       business, good will, franchises and assets so acquired in
                       the stock, bonds or other securities of the Corporation
                       or otherwise.

                 (i)   To carry on any other business which may seem to the
                       Corporation to be calculated directly or indirectly to
                       effectuate the aforesaid objects, or any of them, to
                       facilitate it in the transaction of its aforesaid
                       businesses, or any part thereof, or in the transaction of
                       any other business that may be calculated directly or
                       indirectly to so enhance the value of its property and
                       directly or otherwise of its right; and to have and
                       exercise all powers conferred by the General Laws of the
                       State of Maryland and the Corporations and Associations
                       Article of the





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                       Annotated Code of Maryland, upon corporations formed
                       thereunder, and to exercise and enjoy all powers, rights
                       and privileges granted to or conferred upon corporations
                       of this character by said General Laws and said
                       Corporations and Associations Article, now or hereafter
                       in force; the enumeration of certain powers, as herein
                       specified, not being intended to exclude any such other
                       powers, rights and privileges.

                 (j)   To have one or more offices and places of business and to
                       carry on all or any of its operations and businesses, and
                       without restrictions or limits, as to amount or number,
                       in any of the States, Districts, Territories or Colonies
                       of the United States, and in any and all foreign
                       countries, subject to the laws of such State, District,
                       Territory, Colony or Country.

         The foregoing clauses shall be construed both as objects and powers and
shall be deemed to be cumulative and none of them shall be deemed as restricting
or limiting the other, nor shall the foregoing enumeration of specific powers be
deemed in any way to limit or restrict in any manner the general powers
hereinbefore enumerated or the general powers of the Corporation and the
enjoyment thereof as conferred by law.

         FOURTH: The post office address of the principal office of the
Corporation is 1901 Sulphur Spring Road, Baltimore, Maryland 21227. The name and
post office address of the Resident Agent of the Corporation in this State is
David B. Rudow, 600 Mercantile Bank & Trust Building, 2 Hopkins Plaza,
Baltimore, Maryland 21201, an individual actually residing in this State.





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         FIFTH: The total number of shares of stock which the Corporation has
authority to issue is one thousand (1,000) shares of common stock, all of one
class, with no nominal or par value.

         SIXTH: The number of Directors of the Corporation shall be two (2),
which number may be increased or decreased pursuant to the By-Laws of the
Corporation, provided that any such increase or decrease in the number of
Directors shall conform with the requirements of the laws of the State of
Maryland. The names of the Directors who shall act until the first annual
meeting of Stockholders or until their successors are duly chosen and qualify
are: Selvin Passen, M.D. and Jacob M. Schorr, Ph.D.

         SEVENTH: The following provisions are hereby adopted for the purpose of
defining, limiting and regulating the powers of the Corporation and of the
Directors and Stockholders:

                 (a)   The Board of Directors of the Corporation is hereby
                       empowered to authorize, from time to time, the issuance
                       of shares of the Common Stock of the Corporation, of no
                       par value for such consideration as the Board of
                       Directors may deem advisable, provided that when the
                       consideration is other than money, the Board of Directors
                       shall state by resolution its opinion of the actual value
                       thereof. The Board of Directors shall have full power and
                       authority to determine, from time to time, what part of
                       the consideration received upon the issue of Common
                       Stock, without par value, shall constitute capital and
                       what part surplus.

                 (b)   Agreements may be entered into by any Stockholder or
                       Stockholders giving to the Corporation or to any other
                       Stockholder or Stockholders an option to purchase the
                       stockholdings of such Stockholder or Stockholders, and
                       binding such Stockholder or Stockholders, his or their
                       heirs, executors,





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                       administrators and assigns, and the shares of stock of
                       such person or persons shall, thereupon, be subject to
                       such agreement and transferable only upon proof of
                       compliance therewith; provided, however, such agreement
                       be filed with the Corporation, and reference thereto be
                       placed upon the Certificates of Stock.

                 (c)   The Board of Directors shall have the power, from time to
                       time, to fix, determine and vary the amount of working
                       capital of the Corporation and to determine what part of
                       the surplus and retained earnings of the Corporation, if
                       any, or of the net profits of the Corporation, if any,
                       shall be declared as dividends and paid in cash, in kind
                       or in any combination thereof, to the Stockholders.

         EIGHTH: To the maximum extent that Maryland law in effect from time to
time permits limitation of the liability of directors and officers, no director
or officer of the Corporation shall be liable to the Corporation or its
stockholders for money damages. Neither the amendment nor repeal of this
Article, nor the adoption or amendment of any other provision of the Charter or
By-Laws inconsistent with this Article, shall apply to or affect in any respect
the applicability of the preceding sentence with respect to any act or failure
to act which occurred prior to such amendment, repeal or adoption.

         NINTH:            The duration of the Corporation shall be perpetual.

         IN WITNESS WHEREOF, I have signed these Articles of Incorporation this
16th day of February, 1993, and I acknowledge the same to be my act.

WITNESS:

/s/ William Galvin                               /s/ David B. Rudow       (SEAL)
- ------------------                              ------------------------
                                                David B. Rudow