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                                                                     EXHIBIT 4.2

                        MISSISSIPPI CHEMICAL CORPORATION
                              AMENDED AND RESTATED
                            1994 STOCK INCENTIVE PLAN

         1. Purpose. The purpose of this Stock Incentive Plan (the "Plan") is to
enable Mississippi Chemical Corporation (the "Company") to offer certain
officers and other key employees of the Company and its subsidiaries
performance-based incentives and other equity interests in the Company, thereby
attracting, retaining and rewarding such employees and strengthening the
mutuality of interest between such employees and the Company's shareholders.

         2. Administration. The Plan shall be administered by the Compensation
Committee of the Board of Directors of the Company (the "Board of Directors") or
by such other committee of the Board of Directors designated by the Board of
Directors for such purpose. The Compensation or other Committee administering
this Plan (the "Committee") shall be comprised solely of two or more individuals
who are each a "nonemployee director" as defined in Rule 16b-3 under the
Securities Exchange Act of 1934, as amended (the "Exchange Act"), and also an
"outside director" within the meaning of Treasury Regulation
Section 1.162-27(e)(3) (the "Committee"). The Committee will approve the forms
of agreements relating to the benefits granted hereunder, containing such terms
and conditions consistent with the provisions of this Plan as are determined by
the Committee, which agreements may be executed on behalf of the Company by the
Chief Executive Officer or any Vice President of the Company. Notwithstanding
the foregoing, the Committee shall have exclusive authority to make and
administer grants to individuals who are or may reasonably be expected to become
"covered employees," as defined in Section 162(m) (3) of the Internal Revenue
Code of 1986, as amended from time to time (the "Code"), which are intended to
qualify as performance-based compensation under Code Section 162(m)(4)(C).

         The Committee will have complete authority to construe, interpret and
administer the provisions of this Plan and the provisions of the agreements
relating to the benefits granted hereunder; to prescribe, amend and rescind
rules and regulations pertaining to this Plan; and to make all other
determinations necessary or deemed advisable in the administration of the Plan.
The determinations, interpretations and constructions made by the Committee are
final and conclusive. No member of the Committee may be held liable for any
action taken, or failed to be taken, made in good faith relating to the Plan or
any benefit hereunder, and the members of the Committee will be entitled to
defense, indemnification and reimbursement by the Company in respect of any
claim, loss, damage or expense (including attorneys' fees) arising therefrom to
the fullest extent permitted by law and by the Articles of Incorporation of the
Company. Except to the extent prohibited by applicable law or the applicable
rule of a stock exchange, the Committee may delegate all or any part of its
responsibilities and powers with respect to nonofficer participants to the Chief
Executive Officer of the Company or any other person selected by it, which
delegation may be revoked at any time.

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         3. Eligibility. Benefits under the Plan may be granted to any officer
or other key employee of the Company or one of its subsidiaries on the basis of
the special importance of their services in the management, development and/or
operations of the Company and its subsidiaries. For these purposes, a subsidiary
includes any corporation, partnership or other entity that is a "subsidiary
corporation" (as that term is defined in Code Section 424(f)) with respect to
the Company.

         4. Benefits. The benefits that may be granted under the Plan consist of
(a) stock options, (b) stock appreciation rights, and (c) stock awards.

         5. Shares Reserved. There is hereby reserved for issuance under the
Plan an aggregate of 3,400,000 shares of common stock of the Company, subject to
adjustment pursuant to Section 13 below, which may be authorized but unissued or
treasury shares. All of such shares may, but need not, be issued pursuant to the
exercise of incentive stock options. The maximum number of shares that may be
covered by benefits granted to any one participant in any fiscal year is 200,000
shares, subject to adjustment pursuant to Section 13 below. No more than 160,000
shares, subject to adjustment pursuant to Section 13 below, may be issued as
stock awards hereunder. If there is a lapse, expiration, termination or
cancellation of any option prior to the issuance of shares thereunder, or if
shares are issued and thereafter are reacquired by the Company pursuant to
rights reserved upon issuance thereof, those shares may again be used for new
awards under this Plan. Notwithstanding the foregoing, subject to adjustment
pursuant to Section 13 below, no more than 200,000 shares may be subject to
stock options or stock appreciation rights that are intended to be
"performance-based compensation," as that term is used in Section 162(m) of the
Code, granted to any one participant in any fiscal year; solely for purposes of
this limitation, options or stock appreciation rights that are cancelled
continue to count against the limit, and options or stock appreciation rights
that are repriced are treated as if they had been cancelled and new grants made.

         6. Stock Options. Stock options shall consist of options to purchase
shares of common stock of the Company. Certain options granted under this Plan
are intended to qualify as "incentive stock options" pursuant to Code Section
422, while certain other options granted under the Plan will constitute
nonqualified options, in each case as determined by the Committee. The exercise
price for any stock option shall be not less than 100% of the fair market value
of the common stock of the Company on the date the stock option is granted;
provided, however, that, if the participant owns on the date of grant more than
10% of the total combined voting power of all classes of stock of the Company or
its parent or any of its subsidiaries (a "10% Holder"), as more fully described
in Section 422(b) (6) of the Code or any successor provision, the exercise price
for any incentive stock option granted to the 10% Holder must not be less than
110% of the fair market value of the common stock of the Company on the date of
grant. The aggregate fair market value (determined as of the time the stock
option is granted) of the shares of common stock with respect to which incentive
stock options are exercisable for the first time by a participant during any
calendar year (under all plans of the employer of such participant and its
parent and subsidiary corporations as defined in Section 424 (e) and (f) of the
Code, or a corporation or a parent or subsidiary corporation of such corporation
issuing or assuming a stock option in a transaction to which Section 424(a) of
the Code applies) may not exceed $100,000 or such other amount as from time to
time provided in Section 422(d) of the Code or any successor provision.

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         Upon exercise, the exercise price may be paid by check or, in the
discretion of the Committee, by the delivery of shares of common stock of the
Company then owned by the participant. A participant may also use cashless
exercise as permitted under Regulation T, 12 CFR Part 220, or any successor
provision ("Regulation T"), if the shares to be purchased are covered by an
effective registration statement under the Securities Act of 1933, as amended.
Under Regulation T, any stock option granted under the Plan may be exercised by
a broker-dealer acting on behalf of a participant if (a) the broker-dealer has
received from the participant or the Company a fully- and duly-endorsed
agreement evidencing such stock option, together with instructions signed by the
participant requesting the Company to deliver the shares subject to such stock
option to the broker-dealer on behalf of the participant and specifying the
account into which such shares should be deposited, (b) adequate provision has
been made with respect to the payment of any withholding taxes due upon such
exercise, and (c) the broker-dealer and the participant have otherwise complied
with Section 220.3 (e) (4) of Regulation T.

         Stock options will become exercisable at such time or times and subject
to such terms and conditions as may be determined by the Committee at the time
of grant; provided, however, that no stock option may be exercisable prior to
six months after the option grant date and no incentive stock option may be
exercisable later than ten years after the grant date, or five years for any
incentive stock option granted to a 10% Holder. The terms and conditions under
which a benefit may be exercised after a participant's termination of employment
will be determined by the Committee, except as otherwise provided herein. The
conditions under which such post-termination exercises may be permitted with
respect to incentive stock options must be determined in accordance with the
provisions of Section 422 of the Code and as otherwise provided in this Section
6 above.

         7. Stock Appreciation Rights. Stock appreciation rights may be granted
in conjunction with the grant of any nonqualified stock option granted hereunder
and shall be subject to such terms and conditions consistent with the Plan as
the Committee shall impose from time to time, including the following:

                  (a) A stock appreciation right may be granted with respect to
         a stock option at the time of its grant or at any time thereafter up to
         six months prior to its expiration;

                  (b) Stock appreciation rights will permit the holder to
         surrender any related stock option or portion thereof which is then
         exercisable and elect to receive in exchange therefor cash in an amount
         equal to:

                  (i) The excess of the fair market value on the date
                  of such election of one share of common stock over the option
                  price, multiplied by

                  (ii) The number of shares issuable upon exercise of
                  such option or portion thereof which is so surrendered.

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                  (c) The Committee shall satisfy a participant's right to
         receive the amount of cash determined under paragraph (b) hereof in
         whole or in part by delivering shares of the common stock of the
         Company equal in value to such amount as of the date of the
         participant's election.

                  (d) In the event of the exercise of a stock appreciation
         right, the number of shares reserved for issuance hereunder shall be
         reduced by the number of shares covered by the stock option or portion
         thereof surrendered.

         8. Stock Awards. Stock awards will consist of the grant of shares of
common stock of the Company to participants without other payment therefor as
additional compensation for their services to the Company or one of its
subsidiaries. A stock award shall be subject to such terms and conditions as the
Committee determines appropriate including, without limitation, restrictions on
the sale or other disposition of such shares, the right of the Company to
reacquire such shares upon termination of the participant's employment within
specified periods and conditions requiring that the shares be earned in whole or
in part upon the achievement of performance goals or other objective criteria
established by the Committee over a designated period of time. The Committee may
designate whether the grant of any stock award is intended to be
"performance-based compensation," as that term is used in Section 162(m) of the
Code, which stock award must be conditioned on the achievement of one or more
performance measures established by the Committee. The performance measures
established by the Committee may include earnings per share, total return on
shareholder equity, or such other goals as may be established by the Committee
in its discretion. For stock awards intended to be "performance-based
compensation," the grant of the stock award and the establishment of the
performance measures must be made during the period required under Section
162(m) of the Code.

         9. Transferability. Incentive stock options granted under this Plan may
not be transferred other than by will or the laws of descent and distribution,
and each incentive stock option may be exercised during the participant's
lifetime only by the participant or the participant's guardian or legal
representative. Participants may transfer nonqualified stock options and stock
awards only as provided by the Committee.

         10. Change in Control. In the event of a change in control of the
Company, all outstanding stock options and stock appreciation rights shall
become immediately exercisable and all stock awards shall immediately vest with
all performance goals deemed fully achieved. For these purposes, change in
control means the occurrence of any of the following events, as a result of one
transaction or a series of transactions:

                  (a) any "person" (as that term is used in Sections 13(d) and
         14(d) of the Exchange Act, but excluding the Company, its affiliates
         and any qualified or nonqualified plan maintained by the Company or its
         affiliates) becomes the "beneficial owner" (as defined in Rule 13d-3
         promulgated under the Exchange Act), directly or indirectly, of

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         securities of the Company representing more than 20% of the combined
         voting power of the Company's then outstanding securities;

                  (b) individuals who constitute a majority of the Board of
         Directors immediately prior to a contested election for positions on
         the Board of Directors cease to constitute a majority as a result of
         such contested election;

                  (c) the Company is combined (by merger, share exchange,
         consolidation, or otherwise) with another entity and, as a result of
         such combination, less than 75% of the outstanding securities of the
         surviving or resulting entity are owned in the aggregate by the former
         shareholders of the Company; or

                  (d) the Company sells, leases, or otherwise transfers all or
         substantially all of its properties or assets to another person or
         entity.

Notwithstanding the foregoing, benefits payable on a change of control shall be
limited so that no excess parachute payments, as defined in Code Section 280G(b)
(1), occur in accordance with such additional provisions as the Committee
includes in the award pursuant to Section 11 below.

         11. Other Provisions. The award of any benefit under the Plan may also
be subject to other provisions (whether or not applicable to the benefit awarded
to any other participant) as the Committee determines appropriate, including
such provisions as may be required to comply with federal or state securities
laws and stock exchange requirements and understandings or conditions as to the
participant's employment.

         12. Fair Market Value. The fair market value of the Company's common
stock at any time shall be determined in such manner as the Committee may deem
equitable or as required by applicable law or regulation.

         13. Adjustment Provisions.

                  (a) If the Company at any time changes the number of issued
         shares of common stock without new consideration to the Company (such
         as by stock dividend or stock split), the total number of shares
         reserved for issuance under this Plan and the number of shares covered
         by each outstanding benefit hereunder shall be adjusted to the number
         of shares as is equitably required, together with an appropriate
         adjustment to the exercise price of stock options so that the aggregate
         consideration payable to the Company, if any, upon exercise of such
         option will not be changed.

                  (b) Notwithstanding any other provision of this Plan, and
         without affecting the number of shares reserved or available hereunder,
         the Board of Directors may authorize the issuance or assumption of
         benefits in connection with any merger, consolidation, acquisition of
         property or stock, or reorganization upon such terms and conditions as
         it may deem appropriate.

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                  (c) In the event of any merger, consolidation or
         reorganization of the Company with any other entity, there may be
         substituted, on an equitable basis as determined by the Committee, for
         each share of common stock then reserved for issuance under the Plan
         and for each share of common stock then subject to a benefit granted
         under the Plan, the number and kind of shares of stock, other
         securities, cash or other property to which holders of common stock of
         the Company will be entitled pursuant to the transaction.

         14. Taxes. The Company shall be entitled to withhold the amount of any
tax attributable to any shares deliverable under the Plan after giving the
person entitled to receive the shares notice as far in advance as practicable
and the Company may defer making delivery as to any benefit if any such tax is
payable until indemnified to its satisfaction. The Committee may, in its
discretion and subject to rules that it may adopt, permit a participant to pay
all or a portion of the taxes arising in connection with any benefit under the
Plan by electing to have the Company withhold shares of common stock from the
shares otherwise deliverable to the participant, having a fair market value
equal to the amount to be withheld.

         15. Term of Plan; Amendment, Modification or Cancellation of Benefits.
The Plan will be unlimited in duration and, in the event of termination of the
Plan, will remain in effect as long as any benefits granted hereunder remain
outstanding; provided, however, that no incentive stock option may be granted
more than ten years after the date of the approval of this Plan by the
shareholders of the Company, or the date of approval of this amendment and
restatement for incentive stock options granted based upon the increase in
shares affected by such amendment and restatement. The terms and conditions
applicable to any benefits granted prior to termination of the Plan may at any
time be amended or cancelled by mutual agreement between the Committee and the
participant or any other persons as may then have an interest therein and may be
unilaterally modified by the Committee whenever such modification is deemed
necessary to protect the Company or its shareholders.

         16. Amendment or Discontinuation of Plan. The Board of Directors may
amend the Plan at any time, provided that no such amendment shall be effective
unless approved within 12 months after the date of the adoption of such
amendment by the affirmative vote of a majority of the shareholders. The Board
of Directors may suspend the Plan or discontinue the Plan at any time; provided,
however, that no such action may adversely affect any outstanding benefit.

         17. Shareholder Approval. The Plan was adopted by the Board of
Directors on August 2, 1994, and was approved by the shareholders on November 9,
1994. This amendment and restatement of the Plan was adopted by the Board of
Directors on July 22, 1999, subject to shareholder approval. This amendment and
restatement of the Plan and any benefits granted based upon such amendment and
restatement will be null and void if shareholder approval is not obtained at the
next annual meeting of shareholders.<PAGE>   1

                                                                    EXHIBIT 10.1

                       SECOND AMENDMENT TO PROMISSORY NOTE

      SECOND AMENDMENT TO PROMISSORY NOTE dated as of the 12th day of November,
1999 by and between RAYMOND C. KUBACKI, JR. ( "Kubacki") and PSYCHEMEDICS
CORPORATION (the "Company").

      WHEREAS, Kubacki and the Company entered into a Promissory Note dated
November 12, 1997, (the "Note") in the original principal amount of Two Hundred
Eleven Thousand Two Hundred Thirty-two Dollars ($211,232.00); and

      WHEREAS, Kubacki and the entered into a First Amendment to the Note on
November 12, 1998; and

      WHEREAS, the Company has agreed to extend the repayment of $196,991,76 of
the principal balance of the Note; and

      WHEREAS, Kubacki's obligations under the Note are secured by a pledge of
shares of Common Stock of the Company pursuant to a Pledge Agreement dated
November 12, 1997 (the "Pledge Agreement");

      NOW, THEREFORE, for valuable consideration, the receipt and sufficiency of
which is hereby acknowledged, the parties hereto hereby agree as follows:

      1. AMENDMENT. (a) The Note, as amended, is hereby further amended by
deleting the first three paragraphs thereof and inserting in lieu thereof the
following:

                "FOR VALUE RECEIVED, the undersigned RAYMOND C. KUBACKI, JR.
      hereby promises to pay to the order of PSYCHEMEDICS CORPORATION, a
      Delaware corporation (the "Company"), in accordance with and subject to
      the terms and conditions set forth herein, on or before November 12, 2000,
      the principal sum of ONE HUNDRED NINETY-SIX THOUSAND NINE HUNDRED
      NINETY-ONE AND 76/100 DOLLARS ($196,991.76), or so much thereof as may
      from time to time be outstanding, and to pay interest on the unpaid
      portion of such principal amount at the rate of 5.82% PER ANNUM until such
      principal amount and all accrued unpaid interest thereon shall have been
      paid.

                Interest accrued on the unpaid balance of principal from time to
      time outstanding shall be payable together with payment of principal. Each
      payment made under this Note shall be applied first to interest then due
      and then to principal.

                This Note is secured by a pledge of certain shares of Common
      Stock of the Company owned by the undersigned more particularly described
      in the Pledge Agreement dated November 12, 1997 (the "Pledge Agreement")
      by and between the undersigned and the Company. The Pledge Agreement is
      intended to provide additional security to the Company for the obligations
      of the undersigned under this Note and is not intended to limit in any way
      the obligations of the undersigned under this Note which is a full
      recourse obligation of the undersigned."

                                       1

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      (b) All references in the Pledge Agreement to the Note shall be deemed to
refer to the Note, as modified and amended hereby.

      2. RATIFICATION. (a) The terms and provisions of the Note, as modified and
amended hereby, are hereby ratified and confirmed by Kubacki in all respects and
the Note shall remain in full force and effect in accordance with its terms as
so modified and amended.

      (b) The obligations of Kubacki to repay to the Company all indebtedness
under the Note, as modified and amended hereby, and to pay and perform all of
its other obligations to the Company are and will continue to be secured by the
Pledge Agreement and the Company is and will continue to be entitled to the
benefit of all of the rights and remedies thereunder.

      (c) Nothing herein is intended or shall be construed so as to discharge,
release, terminate, or otherwise limit or modify any indebtedness, obligations,
or liabilities of Kubacki or any collateral security therefor.

      3. MISCELLANEOUS. This First Amendment to Promissory Note shall be
governed by the laws of the Commonwealth of Massachusetts, shall be construed as
a sealed instrument, and shall be binding upon, and inure to the benefit of, the
parties hereto and their respective successors and assigns.

      Executed as a sealed instrument as of the date set forth above.

                               PSYCHEMEDICS CORPORATION

                               By: /s/ Peter Monson
                                   ---------------------------------------------
                                   Peter Monson, Vice President

                                   /s/ Raymond C. Kubacki, Jr.
                                   ---------------------------------------------
                                   Raymond C. Kubacki, Jr.

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