<PAGE>   1
                                                                    EXHIBIT 10.6


                                MEDIBUY.COM, INC.

                 1999 NON-EMPLOYEE DIRECTORS' STOCK OPTION PLAN

                           ADOPTED DECEMBER 14, 1999
                 APPROVED BY STOCKHOLDERS _______________, _____
                       EFFECTIVE DATE: DECEMBER 14, 1999
                             TERMINATION DATE: NONE

1.       PURPOSES.

         (a) ELIGIBLE OPTION RECIPIENTS. The persons eligible to receive Options
are the Non-Employee Directors of the Company.

         (b) AVAILABLE OPTIONS. The purpose of the Plan is to provide a means by
which Non-Employee Directors may be given an opportunity to benefit from
increases in value of the Common Stock through the granting of Nonstatutory
Stock Options.

         (c) GENERAL PURPOSE. The Company, by means of the Plan, seeks to retain
the services of its Non-Employee Directors, to secure and retain the services of
new Non-Employee Directors and to provide incentives for such persons to exert
maximum efforts for the success of the Company and its Affiliates.

2.       DEFINITIONS.

         (a) "AFFILIATE" means any parent corporation or subsidiary corporation
of the Company, whether now or hereafter existing, as those terms are defined in
Sections 424(e) and (f), respectively, of the Code.

         (b) "ANNUAL GRANT" means an Option granted annually to all Non-Employee
Directors who meet the criteria specified in subsection 6(b) of the Plan.

         (c) "ANNUAL MEETING" means the annual meeting of the stockholders of
the Company.

         (d) "BOARD" means the Board of Directors of the Company.

         (e) "CODE" means the Internal Revenue Code of 1986, as amended.

         (f) "COMMON STOCK" means the common stock of the Company.

         (g) "COMPANY" means MEDIBUY.COM, INC., a Delaware corporation.

         (h) "CONSULTANT" means any person, including an advisor, (i) engaged by
the Company or an Affiliate to render consulting or advisory services and who is
compensated for



                                      1.
<PAGE>   2

such services or (ii) who is a member of the Board of Directors of an Affiliate.
However, the term "Consultant" shall not include either Directors of the Company
who are not  compensated  by the Company  for their  services  as  Directors  or
Directors of the Company who are merely paid a director's fee by the Company for
their services as Directors.

         (i) "CONTINUOUS SERVICE" means that the Optionholder's service with the
Company or an Affiliate, whether as an Employee, Director or Consultant, is not
interrupted or terminated. The Optionholder's Continuous Service shall not be
deemed to have terminated merely because of a change in the capacity in which
the Optionholder renders service to the Company or an Affiliate as an Employee,
Consultant or Director or a change in the entity for which the Optionholder
renders such service, provided that there is no interruption or termination of
the Optionholder's Continuous Service. For example, a change in status from a
Non-Employee Director of the Company to a Consultant of an Affiliate or an
Employee of the Company will not constitute an interruption of Continuous
Service. The Board or the chief executive officer of the Company, in that
party's sole discretion, may determine whether Continuous Service shall be
considered interrupted in the case of any leave of absence approved by that
party, including sick leave, military leave or any other personal leave.

         (j) "DIRECTOR" means a member of the Board of Directors of the Company.

         (k) "DISABILITY" means the permanent and total disability of a person
within the meaning of Section 22(e)(3) of the Code.

         (l) "EMPLOYEE" means any person employed by the Company or an
Affiliate. Mere service as a Director or payment of a director's fee by the
Company or an Affiliate shall not be sufficient to constitute "employment" by
the Company or an Affiliate.

         (m) "EXCHANGE ACT" means the Securities Exchange Act of 1934, as
amended.

         (n) "FAIR MARKET VALUE" means, as of any date, the value of the Common
Stock determined as follows:

                  (i) If the Common Stock is listed on any established stock
exchange or traded on the Nasdaq National Market or the Nasdaq SmallCap Market,
the Fair Market Value of a share of Common Stock shall be the closing sales
price for such stock (or the closing bid, if no sales were reported) as quoted
on such exchange or market (or the exchange or market with the greatest volume
of trading in the Common Stock) on the last market trading day prior to the day
of determination, as reported in The Wall Street Journal or such other source as
the Board deems reliable.

                  (ii) In the absence of such markets for the Common Stock, the
Fair Market Value shall be determined in good faith by the Board.

                  (iii) On the IPO Date, the Fair Market Value of a share of
Common Stock shall be the price offered to the public without taking into
account any underwriters' commissions or discounts.



                                       2.
<PAGE>   3

         (o) "INITIAL GRANT" means an Option granted to a Non-Employee Director
who meets the criteria specified in subsection 6(a) of the Plan.

         (p) "IPO DATE" means the effective date of the initial public offering
of the Common Stock.

         (q) "NON-EMPLOYEE DIRECTOR" means a Director who is not an Employee.

         (r) "NONSTATUTORY STOCK OPTION" means an Option not intended to qualify
as an incentive stock option within the meaning of Section 422 of the Code and
the regulations promulgated thereunder.

         (s) "OFFICER" means a person who is an officer of the Company within
the meaning of Section 16 of the Exchange Act and the rules and regulations
promulgated thereunder.

         (t) "OPTION" means a Nonstatutory Stock Option granted pursuant to the
Plan.

         (u) "OPTION AGREEMENT" means a written agreement between the Company
and an Optionholder evidencing the terms and conditions of an individual Option
grant. Each Option Agreement shall be subject to the terms and conditions of the
Plan.

         (v) "OPTIONHOLDER" means a person to whom an Option is granted pursuant
to the Plan or, if applicable, such other person who holds an outstanding
Option.

         (w) "PLAN" means this MEDIBUY.COM,  INC. 1999  Non-Employee  Directors'
Stock Option Plan.

         (x) "RULE 16b-3" means Rule 16b-3 promulgated under the Exchange Act or
any successor to Rule 16b-3, as in effect from time to time.

         (y) "SECURITIES ACT" means the Securities Act of 1933, as amended.

3.       ADMINISTRATION.

         (a) ADMINISTRATION BY BOARD. The Board shall administer the Plan. The
Board may not delegate administration of the Plan to a committee.

         (b) POWERS OF BOARD. The Board shall have the power, subject to, and
within the limitations of, the express provisions of the Plan:

                  (i) To determine the provisions of each Option to the extent
not specified in the Plan.

                  (ii) To construe and interpret the Plan and Options granted
under it, and to establish, amend and revoke rules and regulations for its
administration. The Board, in the exercise of this power, may correct any
defect, omission or inconsistency in the Plan or in any



                                       3.
<PAGE>   4

Option  Agreement,  in a manner  and to the extent it shall  deem  necessary  or
expedient to make the Plan fully effective.

                  (iii) To amend the Plan or an Option as provided in Section
12.

                  (iv) Generally, to exercise such powers and to perform such
acts as the Board deems necessary or expedient to promote the best interests of
the Company that are not in conflict with the provisions of the Plan.

         (c) EFFECT OF BOARD'S DECISION. All determinations, interpretations and
constructions made by the Board in good faith shall not be subject to review by
any person and shall be final, binding and conclusive on all persons.

4.       SHARES SUBJECT TO THE PLAN.

         (a) SHARE RESERVE. Subject to the provisions of Section 11 relating to
adjustments upon changes in the Common Stock, the Common Stock that may be
issued pursuant to Options shall not exceed in the aggregate One Hundred Fifty
Thousand (150,000) shares of Common Stock plus an annual increase to be added on
the day of each Annual Stockholders Meeting beginning with the Annual
Stockholders Meeting in 2001, equal to the least of (i) one-tenth of one percent
(.1%) of the Company's outstanding shares on each such date (rounded to the
nearest whole share and calculated on a fully diluted basis, that is assuming
the exercise of all outstanding stock options and warrants to purchase common
stock), (ii) 25,000 shares or (iii) an amount determined by the Board. If any
right granted under the Plan shall for any reason terminate without having been
exercised, the Common Stock not purchased under such right shall again become
available for the Plan.

         (b) REVERSION OF SHARES TO THE SHARE RESERVE. If any Option shall for
any reason expire or otherwise terminate, in whole or in part, without having
been exercised in full, the shares of Common Stock not acquired under such
Option shall revert to and again become available for issuance under the Plan.

         (c) SOURCE OF SHARES. The shares of Common Stock subject to the Plan
may be unissued shares or reacquired shares, bought on the market or otherwise.

5.       ELIGIBILITY.

         The  Options as set forth in section 6  automatically  shall be granted
under the Plan to all Non-Employee Directors.

6.       NON-DISCRETIONARY GRANTS.

         (a)  INITIAL  GRANTS.  Without  any  further  action  of the  Board,
and subject to the provisions of Section 11 relating to adjustments upon
changes in the Common Stock, a Non-Employee Director shall be granted the an
Initial Grant as follows:



                                       4.
<PAGE>   5
                  (i) After the IPO Date, each person who is elected or
appointed for the first time to be a Non-Employee Director automatically shall,
upon the date of his or her initial election or appointment to be a Non-Employee
Director by the Board or stockholders of the Company, be granted an Initial
Grant to purchase Seven Thousand Five Hundred (7,500) shares of Common Stock on
the terms and conditions set forth herein.

         (b) ANNUAL GRANTS. Without any further action of the Board, and subject
to the provisions of Section 11 relating to adjustments upon changes in the
Common Stock, a Non-Employee Director shall be granted an Annual Grant as
follows: On the day following each Annual Meeting commencing with the Annual
Meeting in 2001, each person who is then a Non-Employee Director automatically
shall be granted an Annual Grant to purchase Two Thousand Five Hundred (2,500)
shares of Common Stock on the terms and conditions set forth herein; provided,
however, that if the person has not been serving as a Non-Employee Director for
the entire period since the preceding Annual Meeting, then the number of shares
subject to the Annual Grant shall be reduced pro rata for each full quarter
prior to the date of grant during which such person did not serve as a
Non-Employee Director.

7.       OPTION PROVISIONS.

         Each Option shall be in such form and shall contain such terms and
conditions as required by the Plan. Each Option shall contain such additional
terms and conditions, not inconsistent with the Plan, as the Board shall deem
appropriate. Each Option shall include (through incorporation of provisions
hereof by reference in the Option or otherwise) the substance of each of the
following provisions:

         (a) TERM. No Option shall be  exercisable  after the  expiration of ten
(10) years from the date it was granted.

         (b) EXERCISE PRICE. The exercise price of each Option shall be one
hundred percent (100%) of the Fair Market Value of the stock subject to the
Option on the date the Option is granted. Notwithstanding the foregoing, an
Option may be granted with an exercise price lower than that set forth in the
preceding sentence if such Option is granted pursuant to an assumption or
substitution for another option in a manner satisfying the provisions of Section
424(a) of the Code.

         (c) CONSIDERATION. The purchase price of stock acquired pursuant to an
Option may be paid, to the extent permitted by applicable statutes and
regulations, in any combination of the following methods:

                  (i) By cash or check.



                                       5.
<PAGE>   6

                  (ii) Provided that at the time of exercise the Common Stock is
publicly traded and quoted regularly in The Wall Street Journal, by delivery of
already-owned shares of Common Stock either that the Optionholder has held for
the period required to avoid a charge to the Company's reported earnings
(generally six months) or that the Optionholder did not acquire, directly or
indirectly from the Company, that are owned free and clear of any liens, claims,
encumbrances or security interests, and that are valued at Fair Market Value on
the date of exercise. "Delivery" for these purposes shall include delivery to
the Company of the Optionholder's attestation of ownership of such shares of
Common Stock in a form approved by the Company. Notwithstanding the foregoing,
the Optionholder may not exercise the Option by tender to the Company of Common
Stock to the extent such tender would violate the provisions of any law,
regulation or agreement restricting the redemption of the Company's stock.

                  (iii) Provided that at the time of exercise the Common Stock
is publicly traded and quoted regularly in The Wall Street Journal, pursuant to
a program developed under Regulation T as promulgated by the Federal Reserve
Board that, prior to the issuance of Common Stock, results in either the receipt
of cash (or check) by the Company or the receipt of irrevocable instructions to
pay the aggregate exercise price to the Company from the sales proceeds.

         (d) TRANSFERABILITY. An Option is transferable by will or by the laws
of descent and distribution. An Option also is transferable (i) by instrument to
an inter vivos or testamentary trust, in a form accepted by the Company, in
which the Option is to be passed to beneficiaries upon the death of the trustor
(settlor) and (ii) by gift, in a form accepted by the Company, to a member of
the "immediate family" of the Optionholder as that term is defined in 17 C.F.R.
240.16a-1(e). An Option shall be exercisable during the lifetime of the
Optionholder only by the Optionholder and a permitted transferee as provided
herein. However, the Optionholder may, by delivering written notice to the
Company, in a form satisfactory to the Company, designate a third party who, in
the event of the death of the Optionholder, shall thereafter be entitled to
exercise the Option.

         (e) Exercise Schedule. The Option shall be exercisable as the shares of
Common Stock subject to the Option vest.

         (f) VESTING SCHEDULE. Options shall vest as follows:

                  (i) Initial Grants shall provide for vesting of 1/36th of the
shares of Common Stock subject to the Option each month after the date of the
grant of the Option over a period of three (3) years.

                  (ii) Annual Grants shall provide for vesting of 1/36th of the
shares of Common Stock subject to the Option each month after the date of the
grant of the Option over a period of three (3) years.

         (g) TERMINATION OF CONTINUOUS SERVICE. In the event an Optionholder's
Continuous Service terminates (other than upon the Optionholder's death or
Disability), the Optionholder may exercise his or her Option (to the extent that
the Optionholder was entitled to exercise it as



                                       6.
<PAGE>   7

of the date of  termination)  but only  within such period of time ending on the
earlier  of (i) the date  three (3)  months  following  the  termination  of the
Optionholder's  Continuous  Service,  or (ii) the  expiration of the term of the
Option  as set  forth  in the  Option  Agreement.  If,  after  termination,  the
Optionholder  does not exercise his or her Option  within the time  specified in
the Option Agreement, the Option shall terminate.

         (h) EXTENSION OF TERMINATION DATE. If the exercise of the Option
following the termination of the Optionholder's Continuous Service (other than
upon the Optionholder's death or Disability) would be prohibited at any time
solely because the issuance of shares would violate the registration
requirements under the Securities Act, then the Option shall terminate on the
earlier of (i) the expiration of the term of the Option set forth in subsection
7(a) or (ii) the expiration of a period of three (3) months after the
termination of the Optionholder's Continuous Service during which the exercise
of the Option would not be in violation of such registration requirements.

         (i) DISABILITY OF OPTIONHOLDER. In the event an Optionholder's
Continuous Service terminates as a result of the Optionholder's Disability, the
Optionholder may exercise his or her Option (to the extent that the Optionholder
was entitled to exercise it as of the date of termination), but only within such
period of time ending on the earlier of (i) the date twelve (12) months
following such termination or (ii) the expiration of the term of the Option as
set forth in the Option Agreement. If, after termination, the Optionholder does
not exercise his or her Option within the time specified herein, the Option
shall terminate.

         (j) DEATH OF OPTIONHOLDER. In the event (i) an Optionholder's
Continuous Service terminates as a result of the Optionholder's death or (ii)
the Optionholder dies within the three-month period after the termination of the
Optionholder's Continuous Service for a reason other than death, then the Option
may be exercised (to the extent the Optionholder was entitled to exercise the
Option as of the date of death) by the Optionholder's estate, by a person who
acquired the right to exercise the Option by bequest or inheritance or by a
person designated to exercise the Option upon the Optionholder's death, but only
within the period ending on the earlier of (1) the date eighteen (18) months
following the date of death or (2) the expiration of the term of such Option as
set forth in the Option Agreement. If, after death, the Option is not exercised
within the time specified herein, the Option shall terminate.

8.       COVENANTS OF THE COMPANY.

         (a) AVAILABILITY OF SHARES. During the terms of the Options, the
Company shall keep available at all times the number of shares of Common Stock
required to satisfy such Options.

         (b) SECURITIES LAW COMPLIANCE. The Company shall seek to obtain from
each regulatory commission or agency having jurisdiction over the Plan such
authority as may be required to grant Options and to issue and sell shares of
Common Stock upon exercise of the Options; provided, however, that this
undertaking shall not require the Company to register under the Securities Act
the Plan, any Option or any stock issued or issuable pursuant to any such
Option. If, after reasonable efforts, the Company is unable to obtain from any
such regulatory commission or agency the authority which counsel for the Company
deems necessary



                                       7.
<PAGE>   8

for the lawful  issuance and sale of stock under the Plan,  the Company shall be
relieved from any liability for failure to issue and sell stock upon exercise of
such Options unless and until such authority is obtained.

9.       USE OF PROCEEDS FROM STOCK.

         Proceeds from the sale of stock pursuant to Options shall constitute
general funds of the Company.

10.      MISCELLANEOUS.

         (a) STOCKHOLDER RIGHTS. No Optionholder shall be deemed to be the
holder of, or to have any of the rights of a holder with respect to, any shares
subject to such Option unless and until such Optionholder has satisfied all
requirements for exercise of the Option pursuant to its terms.

         (b) NO SERVICE RIGHTS. Nothing in the Plan or any instrument executed
or Option granted pursuant thereto shall confer upon any Optionholder any right
to continue to serve the Company as a Non-Employee Director or shall affect the
right of the Company or an Affiliate to terminate (i) the employment of an
Employee with or without notice and with or without cause, (ii) the service of a
Consultant pursuant to the terms of such Consultant's agreement with the Company
or an Affiliate or (iii) the service of a Director pursuant to the Bylaws of the
Company or an Affiliate, and any applicable provisions of the corporate law of
the state in which the Company or the Affiliate is incorporated, as the case may
be.

         (c) INVESTMENT ASSURANCES. The Company may require an Optionholder, as
a condition of exercising or acquiring stock under any Option, (i) to give
written assurances satisfactory to the Company as to the Optionholder's
knowledge and experience in financial and business matters and/or to employ a
purchaser representative reasonably satisfactory to the Company who is
knowledgeable and experienced in financial and business matters and that he or
she is capable of evaluating, alone or together with the purchaser
representative, the merits and risks of exercising the Option; and (ii) to give
written assurances satisfactory to the Company stating that the Optionholder is
acquiring the stock subject to the Option for the Optionholder's own account and
not with any present intention of selling or otherwise distributing the stock.
The foregoing requirements, and any assurances given pursuant to such
requirements, shall be inoperative if (iii) the issuance of the shares upon the
exercise or acquisition of stock under the Option has been registered under a
then currently effective registration statement under the Securities Act or (iv)
as to any particular requirement, a determination is made by counsel for the
Company that such requirement need not be met in the circumstances under the
then applicable securities laws. The Company may, upon advice of counsel to the
Company, place legends on stock certificates issued under the Plan as such
counsel deems necessary or appropriate in order to comply with applicable
securities laws, including, but not limited to, legends restricting the transfer
of the stock.

         (d) WITHHOLDING OBLIGATIONS. The Optionholder may satisfy any federal,
state or local tax withholding obligation relating to the exercise or
acquisition of stock under an Option



                                       8.
<PAGE>   9
by any of the following  means (in addition to the  Company's  right to
withhold from  any  compensation  paid  to  the  Optionholder  by  the  Company)
or by a combination of such means:  (i) tendering a cash payment;  (ii)
authorizing the Company  to  withhold  shares  from the  shares of the  Common
Stock  otherwise issuable to the Optionholder as a result of the exercise or
acquisition of stock under the Option, provided, however, that no shares of
Common Stock are withheld with a value exceeding the minimum amount of tax
required to be withheld by law; or (iii) delivering to the Company owned and
unencumbered  shares of the Common Stock.

11.      ADJUSTMENTS UPON CHANGES IN STOCK.

         (a) CAPITALIZATION ADJUSTMENTS. If any change is made in the stock
subject to the Plan, or subject to any Option, without the receipt of
consideration by the Company (through merger, consolidation, reorganization,
recapitalization, reincorporation, stock dividend, dividend in property other
than cash, stock split, liquidating dividend, combination of shares, exchange of
shares, change in corporate structure or other transaction not involving the
receipt of consideration by the Company), the Plan will be appropriately
adjusted in the class(es) and maximum number of securities subject both to the
Plan pursuant to subsection 4(a) and to the nondiscretionary Options specified
in Section 5, and the outstanding Options will be appropriately adjusted in the
class(es) and number of securities and price per share of stock subject to such
outstanding Options. The Board shall make such adjustments, and its
determination shall be final, binding and conclusive. (The conversion of any
convertible securities of the Company shall not be treated as a transaction
"without receipt of consideration" by the Company.)

         (b) CHANGE IN CONTROL--DISSOLUTION OR LIQUIDATION. In the event of a
dissolution or liquidation of the Company, then all outstanding Options shall
terminate immediately prior to such event.

         (c) CHANGE IN CONTROL--ASSET SALE, MERGER, CONSOLIDATION OR REVERSE
MERGER. In the event of (i) a sale, lease or other disposition of all or
substantially all of the assets of the Company, (ii) a merger or consolidation
in which the Company is not the surviving corporation or (iii) a reverse merger
in which the Company is the surviving corporation but the shares of Common Stock
outstanding immediately preceding the merger are converted by virtue of the
merger into other property, whether in the form of securities, cash or
otherwise, then any surviving corporation or acquiring corporation shall assume
any Options outstanding under the Plan or shall substitute similar Options
(including an option to acquire the same consideration paid to the stockholders
in the transaction described in this subsection 11(c) for those outstanding
under the Plan). In the event any surviving corporation or acquiring corporation
refuses to assume such Options or to substitute similar Options for those
outstanding under the Plan, then with respect to Options held by Optionholders
whose Continuous Service has not terminated, the vesting of such Options (and
the time during which such Options may be exercised) shall be accelerated in
full, and the Options shall terminate if not exercised at or prior to such
event. With respect to any other Options outstanding under the Plan, such
Options shall terminate if not exercised prior to such event.



                                       9.
<PAGE>   10

12.      AMENDMENT OF THE PLAN AND OPTIONS.

         (a) AMENDMENT OF PLAN. The Board at any time, and from time to time,
may amend the Plan. However, except as provided in Section 11 relating to
adjustments upon changes in stock, no amendment shall be effective unless
approved by the stockholders of the Company to the extent stockholder approval
is necessary to satisfy the requirements of Rule 16b-3 or any Nasdaq or
securities exchange listing requirements.

         (b) STOCKHOLDER APPROVAL. The Board may, in its sole discretion, submit
any other amendment to the Plan for stockholder approval.

         (c) NO IMPAIRMENT OF RIGHTS. Rights under any Option granted before
amendment of the Plan shall not be impaired by any amendment of the Plan unless
(i) the Company requests the consent of the Optionholder and (ii) the
Optionholder consents in writing.

         (d) AMENDMENT OF OPTIONS. The Board at any time, and from time to time,
may amend the terms of any one or more Options; provided, however, that the
rights under any Option shall not be impaired by any such amendment unless (i)
the Company requests the consent of the Optionholder and (ii) the Optionholder
consents in writing.

13.      TERMINATION OR SUSPENSION OF THE PLAN.

         (a) PLAN TERM. The Board may suspend or terminate the Plan at any time.
No Options may be granted under the Plan while the Plan is suspended or after it
is terminated.

         (b) NO IMPAIRMENT  OF RIGHTS.  Suspension  or  termination  of the Plan
shall not impair rights and obligations  under any Option granted while the Plan
is in effect except with the written consent of the Optionholder.

14.      EFFECTIVE DATE OF PLAN.

         The Plan shall become effective on the IPO Date, but no Option shall be
exercised unless and until the Plan has been approved by the stockholders of the
Company, which approval shall be within twelve (12) months before or after the
date the Plan is adopted by the Board.

15.      CHOICE OF LAW.

         All questions concerning the construction, validity and interpretation
of this Plan shall be governed by the law of the State of California, without
regard to such state's conflict of laws rules.


                                      10.