Document:

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Exhibit 4.2

                              FORM OF DEBENTURE
                              -----------------

THIS DEBENTURE AND THE COMMON STOCK ISSUABLE UPON CONVERSION HEREOF HAVE NOT
BEEN REGISTERED PURSUANT TO THE SECURITIES ACT OF 1933, AS AMENDED, AND MAY
BE OFFERED OR SOLD ONLY IF REGISTERED UNDER APPLICABLE SECURITIES LAWS OR IF
AN EXEMPTION THEREFROM IS AVAILABLE. THE SECURITIES ISSUABLE UPON CONVERSION
HEREOF ARE TRANSFERABLE ONLY UPON THE CONDITIONS SPECIFIED IN THE DEBENTURE
PURCHASE AGREEMENT REFERRED TO HEREIN.

                  ZOLTEK COMPANIES, INC.

                  SUBORDINATED CONVERTIBLE DEBENTURE

                  DUE FEBRUARY 13, 2008

$___________                                                February 13, 2003

                  ZOLTEK COMPANIES, INC., a Missouri corporation (the
"Company"), for value received, hereby promises to pay to

                        -----------------------------
                            or registered assigns
                            on February 13, 2008
                           the principal amount of
                             Dollars ($________)

and to pay interest from the date hereof (computed on the basis of a 360-day
year) on the principal amount from time to time remaining unpaid hereon on
each January 1 and July 1 after the date hereof until maturity at the rate
of Seven Percent (7%) per annum.

                  The Company further agrees to pay interest on overdue
principal at the rate per annum equal to two percentage points in excess of
the rate determined in the immediately preceding paragraph (the "Overdue
Rate") until paid and (to the extent legally enforceable) to pay interest on
any overdue installment of interest at the Overdue Rate until paid. The
principal hereof and interest hereon are payable by check mailed to the
address of the holder on the Company's records in coin or currency of the
United States of America which at the time of payment shall be legal tender
for the payment of public and private debts.

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                  This Debenture is issued under and pursuant to the terms
and provisions of a certain Subordinated Convertible Debenture Purchase
Agreement (the "Debenture Agreement"), dated as of February 13, 2003,
entered into by and among the Company, the original purchaser therein
referred to and other purchasers of debentures thereunder (all such
debentures being hereinafter referred to as the "Debentures"), and this
Debenture and the holder hereof are entitled to all the benefits provided
for thereby or referred to therein, to which Debenture Agreement reference
is hereby made for the statement thereof.

                  This Debenture may be declared due prior to its expressed
maturity date if there is an Event of Default (as defined in the Debenture
Agreement) and certain prepayments are required to be made hereon by the
Company all in the events, on the terms and in the manner and amounts as
provided in the Debenture Agreement.

                  As provided in Section 7 of the Debenture Agreement, the
holder of this Debenture shall have the right and option, to convert the
from time to time all, but not less than all, of the unpaid principal amount
hereof, into Common Stock of the Company. Reference is hereby made to
Section 7 of the Debenture Agreement for a full statement of the terms and
conditions relating to such conversion right.

                  This Debenture and the indebtedness evidenced hereby,
including principal and interest shall at all times be and remain junior and
subordinate in right of payment to any and all Indebtedness as defined in
the Debenture Agreement, all in the manner and to the extent as set forth in
the Debenture Agreement.

                  This Debenture is registered on the books of the Company
and is transferable only by surrender thereof at the principal office of the
Company duly endorsed or accompanied by a written instrument of transfer
duly executed by the registered holder of this Debenture or its attorney
duly authorized in writing. Payment of or on account of principal and
interest on this Debenture shall be made only to or upon the order in
writing of the registered holder.

                                        ZOLTEK COMPANIES, INC.

                                        By
                                          ------------------------------------
                                          Name:
                                          Title:

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Exhibit 4.3

                               FORM OF WARRANT
                               ---------------

         THIS SECURITY AND THE SECURITIES ISSUABLE UPON EXERCISE HEREOF HAVE
NOT BEEN REGISTERED UNDER THE SECURITIES ACT OF 1933, AS AMENDED, OR ANY
STATE SECURITIES LAW AND MAY NOT BE TRANSFERRED, SOLD OR OFFERED FOR SALE
UNLESS REGISTERED PURSUANT TO SUCH ACT AND ANY APPLICABLE STATE SECURITIES
LAW OR UNLESS AN EXEMPTION FROM SUCH REGISTRATION IS AVAILABLE.

                                                   Dated:  February 13, 2003

                                   WARRANT
                 TO PURCHASE _______ SHARES OF COMMON STOCK
                                     OF
                           ZOLTEK COMPANIES, INC.

EXPIRING FEBRUARY 13, 2008

         THIS IS TO CERTIFY THAT, for value received, ____________________,
or its registered successors or assigns (the "Holder"), is entitled to
purchase from Zoltek Companies, Inc., a Missouri corporation (the
"Company"), at any time or from time to time after 9:00 a.m., St. Louis,
Missouri time, on the date hereof and prior to 5:00 p.m., St. Louis,
Missouri time, on February 13, 2008 (the "Expiration Date"), at the
principal executive offices of the Company, at the Exercise Price,
______________ (_______) shares of Common Stock, par value $0.01 per share
(the "Common Stock"), of the Company, all subject to adjustment and upon the
terms and conditions as hereinafter provided, and is entitled also to
exercise the other appurtenant rights, powers and privileges hereinafter
described.

         Certain terms used in this Warrant are defined in Article V hereof.
                                                           ---------

                                  ARTICLE I
                             EXERCISE OF WARRANT

         1.1 Method of Exercise. To exercise this Warrant in whole or in
             ------------------
part, the Holder shall deliver to the Company (a) this Warrant, (b) a
written notice, in substantially the form of the Subscription Notice
attached hereto (the "Exercise Notice"), of such Holder's election to
exercise this Warrant, which notice shall specify the number of shares of
Common Stock to be purchased, the denominations of the share certificate or
certificates desired and the name or names in which such certificates are to
be registered, and (c) payment of the Exercise Price with respect to such

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shares. Such payment may be made, at the option of the Holder, by cash,
certified or bank cashier's check or wire transfer.

         The Company shall, as promptly as practicable and in any event
within ten (10) days after receipt of the Exercise Notice, execute and
deliver or cause to be executed and delivered, in accordance with the
Exercise Notice, a certificate or certificates representing the aggregate
number of shares of Common Stock specified in said notice. The share
certificate or certificates so delivered shall be in such denominations as
may be specified in such notice or, if such notice shall not specify
denominations, in denominations of 1,000 shares each, and shall be issued in
the name of the Holder or such other name or names as shall be designated in
such notice. Such certificate or certificates shall be deemed to have been
issued, and such Holder or any other Person so designated to be named
therein, shall be deemed for all purposes to have become a holder of record
of such shares as of the date the aforementioned notice is received by the
Company. If this Warrant shall have been exercised only in part, the Company
shall, at the time of delivery of the certificate or certificates, deliver
to the Holder a new warrant evidencing the rights to purchase the remaining
shares of Common Stock called for by this Warrant, which new warrant shall
in all other respects be identical with this Warrant, as it may from time to
time be amended.

         1.2 Shares To Be Fully Paid, Nonassessable and Registered. All
             -----------------------------------------------------
shares of Common Stock issued upon the exercise of this Warrant shall be
validly issued, fully paid and nonassessable and, if the Common Stock of any
class is then listed on any national securities exchange (as such term is
used in the Exchange Act) or quoted on The Nasdaq Stock Market, upon
issuance all such shares of Common Stock shall be duly listed or quoted
thereon, as the case may be.

         1.3 No Fractional Shares To Be Issued. The Company shall not be
             ---------------------------------
required to issue fractions of shares of Common Stock upon exercise of this
Warrant. If any fraction of a share would, but for this Section 1.3, be
                                                        -----------
issuable upon any exercise of this Warrant, in lieu of such fractional share
the Company shall pay to the Holder, in cash, an amount equal to the same
fraction of the fair market value per share of outstanding Common Stock on
the Business Day immediately prior to the date of such exercise, as
determined in good faith by the Company's Board of Directors.

                                 ARTICLE II
                TRANSFER, EXCHANGE AND REPLACEMENT OF WARRANT

         2.1 Ownership of Warrant. The Company may deem and treat the Person
             --------------------
in whose name this Warrant is registered as the holder and owner hereof
(notwithstanding any notations of ownership or writing hereon made by any
Person other than the Company) for all purposes and shall not be affected by
any notice to the contrary, until presentation of this Warrant for
registration of transfer as provided in this Article II.
                                             ----------

         2.2 Division or Combination of Warrants. This Warrant may be
             -----------------------------------
divided or combined with other warrants upon surrender hereof and of any
warrant or warrants with which this

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Warrant is to be combined at the principal executive offices of the Company,
together with a written notice specifying the names and denominations in
which the new warrant or warrants are to be issued, signed by the holders
hereof and thereof or their respective duly authorized agents or attorneys.
Subject to compliance with Section 2.2 as to any transfer which may be
                           -----------
involved in the division or combination, the Company shall execute and
deliver a new warrant or warrants in exchange for the Warrants to be divided
or combined in accordance with such notice.

         2.3 Loss, Theft, Destruction of Warrant Certificates. Upon receipt
             ------------------------------------------------
of evidence satisfactory to the Company of the loss, theft, destruction or
mutilation of any Warrant and, in the case of any such loss, theft or
destruction, upon receipt of an affidavit of loss which shall include an
indemnification provision satisfactory to the Company, or, in the case of
any such mutilation, upon surrender and cancellation of such Warrant, the
Company will make and deliver, in lieu of such lost, stolen, destroyed or
mutilated Warrant, a new warrant of like tenor representing the right to
purchase the same aggregate number of shares of Common Stock.

         2.4 Expenses of Delivery of Warrant. The Company shall pay all
             -------------------------------
expenses, taxes and other charges payable in connection with the
preparation, issuance and delivery of share certificates of Common Stock
issuable upon exercise of this Warrant and new warrants.

                                 ARTICLE III
                               CERTAIN RIGHTS

         3.1 Delivery of Reports and Information.
             -----------------------------------

                  (a) The Company covenants and agrees with the Holder that
the Company will:

                           (i) Do or cause to be done all things necessary
                  to preserve, renew and keep in full force and effect the
                  Company's legal existence; and

                           (ii) Upon request of the Holder, furnish to the
                  Holder promptly after the same become publicly available,
                  copies of such registration statements, annual, periodic
                  and other reports, and such proxy statements and other
                  information, if any, as shall be filed by the Company with
                  the Securities and Exchange Commission pursuant to the
                  requirements of the Securities Act or the Exchange Act.

                  (b) In case at any time the Company shall declare any
dividend on its Common Stock, whether payable in cash, stock or other
property, then the Company shall give written notice to the Holder of the
date on which the books of the Company shall close or a record shall be
taken for such dividend. Such notice shall also specify the date as of which
the holders of Common Stock of record shall participate in such dividend.
Such written notice shall be given at least twenty (20) days prior to the
action in question, and not more than ninety (90) days and not less than
twenty (20) days prior to the relevant record date or the date fixed for
determining stockholders entitled to participate therein, as the case may
be.

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                                 ARTICLE IV
                           ANTIDILUTION PROVISIONS

         4.1 Adjustments Generally. The Exercise Price and the number of
             ---------------------
shares of Common Stock (or other securities or property) issuable upon
exercise of this Warrant shall be subject to adjustment from time to time
upon the occurrence of certain events, as provided in this Article IV.
                                                           ----------

         4.2 Stock Reorganization and Number of Shares. The Exercise Price
             -----------------------------------------
and the number and kind of securities purchasable upon exercise of this
Warrant shall be subject to adjustment from time to time upon the happening
of certain events as follows: In case the Company shall hereafter (i)
declare a dividend or a distribution on its Common Stock payable in shares
of its Common Stock, (ii) subdivide its outstanding shares of Common Stock,
(iii) combine its outstanding Common Stock into a smaller number of shares,
or (iv) issue other securities of the Company by reclassification of its
Common Stock (including any such reclassification in connection with a
consolidation or merger in which the Company is the continuing corporation),
the number of shares of Common Stock for which this Warrant may be exercised
at the time of the record date for such dividend or distribution or the
effective date of such subdivision, combination or reclassification shall be
proportionately adjusted so that the Holder of any Warrant exercised after
such date shall be entitled to receive the aggregate number and kind of
shares of Common Stock which, if such Warrant had been exercised immediately
prior to such time, the Holder would have owned upon such exercise and been
entitled to receive upon such dividend, distribution, subdivision,
combination or reclassification. Such adjustment shall be made successively
whenever any event listed above shall occur.

         4.3 Merger or Consolidation.
             -----------------------

                  (a) In case of any consolidation or merger of the Company
with or into another corporation (other than a merger in which the Company
is the continuing corporation and which does not result in any
reclassification or change of outstanding shares of the Company's capital
stock issuable upon exercise of this Warrant), or in case of any sale or
conveyance to another corporation of the property, assets, business and
goodwill of the Company as an entirety or substantially as an entirety,
then, as a condition of such consolidation, merger, sale or conveyance, the
Company shall cause lawful and adequate provision to be made by the Company
or such successor or purchasing corporation, as the case may be (such
successor or purchasing corporation thereafter being deemed to be the
Company for the purpose hereof) whereby the Holder shall have the right
thereafter (in lieu of any other right hereunder) to exercise this Warrant
for the kind and amount of shares of stock and other securities and property
receivable upon such consolidation, merger, sale or conveyance by a holder
of the number of shares of Common Stock into which this Warrant might have
been exercised immediately prior to such consolidation, merger, sale or
conveyance. Such provision shall include provision for adjustments which
shall be as nearly equivalent as may be practicable to the adjustments
provided for herein. If, as a result of an adjustment made pursuant hereto,
the Holder upon exercise shall become entitled to receive shares of two or
more classes of Common Stock or

                                   - 4 -

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other capital stock of the Company, the Board of Directors of the Company
(whose determination shall be conclusive) shall determine the allocation of
the adjusted Exercise Price between or among shares of such classes of
capital stock.

                  (b) The Company shall give the Holder written notice of
any proposed merger of the Company or any other corporate reorganization, or
of any sale of all or substantially all of the assets of the Company. Such
notice shall be given not later than twenty (20) days prior to the
stockholders, meeting called to approve such transaction or twenty (20) days
prior to the closing of such transaction, whichever is earlier. Such notice
shall describe the material terms and conditions of the contemplated
transaction and the Company shall thereafter give the Holders prompt notice
of any material changes in such terms and conditions.

                  (c) If subsequent to the giving of notice pursuant to
Section 4.3(b) above but not later than ten (10) days prior to the closing
--------------
of such transaction, the Holder elects to exercise this Warrant, then the
exercise may, at the option of such Holder, be conditioned upon the closing
of such transaction, in which event the person(s) entitled to receive the
Common Stock issuable upon exercise of this Warrant shall not be deemed to
have exercised this Warrant until immediately prior to the closing of such
transaction.

         4.4 No Impairment. The Company will not, by amendment of its
             -------------
Amended and Restated Articles of Incorporation or through any
reorganization, transfer of assets, consolidation, merger, dissolution,
issuance or sale of securities or any other voluntary action, avoid or seek
to avoid the observance or performance of any of the terms to be observed or
performed hereunder by the Company but will at all times in good faith
assist in the carrying out of all the provisions of this Article IV and in
                                                         ----------
the taking of all actions that may be necessary or appropriate to protect
the exercise rights of the Holder.

         4.5 Certificate as to Adjustments. Upon the occurrence of each
             -----------------------------
adjustment or readjustment of the Exercise Price or the number of shares of
Common Stock issuable upon exercise of this Warrant pursuant to this Article
                                                                     -------
IV, the Company at its expense shall promptly compute such adjustment or
--
readjustment in accordance with the terms of this Article IV and furnish to
                                                  ----------
the Holder a certificate setting forth such adjustment or readjustment and
showing in detail the facts upon which such adjustment or readjustment is
based. The Company shall, upon the written request at any time of the
Holder, furnish or cause to be furnished to the Holder a like certificate
setting forth (i) such adjustments and readjustments, (ii) the Exercise
Price in effect at the time, and (iii) the number of shares of Common Stock
and the amount, if any, of other property that would be received at that
time upon exercise of this Warrant.

         4.6 Proceeding Prior to Any Action Requiring Adjustment. As a
             ---------------------------------------------------
condition precedent to the taking of any action which would require an
adjustment pursuant to this Article IV, the Company shall take any action
                            ----------
which may be necessary, including obtaining regulatory approvals or
exemptions, in order that the Company may thereafter validly and legally
issue as fully paid and nonassessable all shares of Common Stock which the
holders of Warrants are entitled to receive upon exercise thereof.

                                   - 5 -

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                                  ARTICLE V
                                 DEFINITIONS

         The following terms, as used in this Warrant, have the following
respective meanings:

         "Business Days" means a day on which the principal national
securities exchange or automated quotation system on which the Common Stock
of the Company is listed or admitted to trading is open for business.

         "Exchange Act" means the Securities Exchange Act of 1934, as
amended, and any successor Federal statute, and the rules and regulations of
the Securities and Exchange Commission (or its successor) thereunder, all as
the same shall be in effect at the time.

         "Exercise Price" means Five Dollars ($5.00) per share of Common
Stock, subject to adjustment pursuant to Article IV.
                                         ----------

         "Person" means an individual partnership, corporation, association,
trust, joint venture, unincorporated organization and any government,
governmental department or agency or political subdivision thereof.

         "Securities Act" means the Securities Act of 1933, as amended, and
any successor Federal statute, and the rules and regulations of the
Securities and Exchange Commission (or its successor) thereunder, all as the
same shall be in effect from time to time.

                                 ARTICLE VI
                                MISCELLANEOUS

         6.1 Notices. Any notice or other communication required by or given
             -------
in connection with this Warrant shall be deemed to be delivered if in
writing (or in the form of a telecopy) addressed as provided below (or to
such other address or telecopy number as may be provided in writing by the
recipient to the other party hereto) and if (a) actually delivered to said
address (b) telecopied to the number of the recipient set forth below before
5:00 p.m. (local time at the recipient's office) on a Business Day, or (c)
in the case of a letter, three Business Days shall have elapsed after the
same shall have been deposited in the United States mails, postage prepaid
and registered or certified:

         If to Company, at:

                  Zoltek Companies, Inc.
                  3101 McKelvey Road
                  St. Louis, Missouri 63044
                  Telecopy: (314) 291-9082
                  Attention: Zsolt Rumy

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         If to Holder at:

                  -------------------
                  -------------------
                  -------------------
                  Telecopy: (___) ________
                  Attention: _________________

         6.2 Waivers; Amendments. No failure or delay of the Holder in
             -------------------
exercising any power or right hereunder shall operate as a waiver thereof,
nor shall any single or partial exercise of such right or power, or any
abandonment or discontinuance of steps to enforce such a right or power,
preclude any other or further exercise thereof or the exercise of any other
right or power. The rights and remedies of the Holder are cumulative and not
exclusive of any rights or remedies which it would otherwise have. The
provisions of this Warrant may be amended, modified or waived with (and only
with) the written consent of the Company and Holder. No notice or demand on
the Company in any case shall entitle the Company to any other or further
notice or demand in similar or other circumstances.

         6.3 Governing Law. This Warrant shall be construed in accordance
             -------------
with and governed by the internal laws of the State of Missouri.

         6.4 Survival of Agreements; Representations and Warranties, Etc.
             ------------------------------------------------------------
All warranties, representations and covenants made by the Company herein or
in any certificate or other instrument delivered by or on behalf of it in
connection with this Warrant shall be considered to have been relied upon by
the Holder and shall survive the issuance and delivery of this Warrant,
regardless of any investigation made by the Holder, and shall continue in
full force and effect so long as this Warrant is outstanding. All statements
in any such certificate or other instrument shall constitute representations
and warranties hereunder.

         6.5 Covenants To Bind Successors and Assigns. All covenants,
             ----------------------------------------
stipulations, promises and agreements in this Warrant contained by or on
behalf of the Company shall bind its successors and assigns.

         6.6 Severability. In case any one or more of the provisions
             ------------
contained in this Warrant shall be invalid, illegal or unenforceable in any
respect, the validity, legality and enforceability of the remaining
provisions contained herein shall not in any way be affected or impaired
thereby.

         6.7 Section Headings. The section headings used herein are for
             ----------------
convenience of reference only, are not part of this Warrant and are not to
affect the construction of or be taken into consideration in interpreting
this Warrant.

         6.8 No Rights as Stockholder. This Warrant shall not entitle the
             ------------------------
Holder to any rights as a stockholder of the Company.

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                  IN WITNESS WHEREOF, Zoltek Companies, Inc. has caused this
Warrant to be executed in its corporate name by one of its officers
thereunto duly authorized, all as of the day and year first above written.

                                        ZOLTEK COMPANIES, INC.

                                        By:  ____________________________
                                        Name: Zsolt Rumy
                                        Title: Chief Executive Officer

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                             SUBSCRIPTION NOTICE

                  (To be executed upon exercise of Warrant)

To:
                  -----------------------------------

         The undersigned hereby irrevocably elects to exercise the right of
purchase represented by the attached Warrant for, and to purchase
thereunder, ________ shares of Common Stock, as provided for therein, and
tenders herewith payment of the Exercise Price in full in the form of cash,
certified or bank cashier's check or wire transfer.

         Please issue a certificate or certificates for such shares of
Common Stock in the following name or names and denominations:

         If said number of shares shall not equal all the shares issuable
upon exercise of the attached Warrant, a new Warrant is to be issued in the
name of the undersigned for the balance remaining of such shares less any
fraction of a share paid in cash.

         Dated:
                 -------------------

                                            ---------------------------------
                                            NOTE: The above signature should
                                                  correspond exactly with
                                                  the name on the face of
                                                  the attached Warrant or
                                                  with the name of the
                                                  assignee appearing in the
                                                  following assignment form.

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                                 ASSIGNMENT

                 (To be executed upon assignment of Warrant)

         For value received, ________________________, hereby sells, assigns
and transfers unto ________________________ the attached Warrant, together
with all right, title and interest therein, and does hereby irrevocably
constitute and appoint ________________________ attorney to transfer said
Warrant on the books of _____________________________, a __________________
corporation, with full power of substitution in the premises.

                                            ----------------------------------
                                            Note: The above signature should
                                                  correspond exactly with
                                                  the name on the face of
                                                  the attached Warrant.

Dated:
        -----------------------

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