Exhibit 4.3


               AMENDMENT NO. 2 TO LOAN AND WARRANT AGREEMENT AND
                         REGISTRATION RIGHTS AGREEMENT



         This AMENDMENT NO. 2 TO LOAN AND WARRANT AGREEMENT AND REGISTRATION
RIGHTS AGREEMENT (this "Amendment") is made and entered into as of December
14, 2006, by and among Zoltek Companies, Inc., a Missouri corporation
("Zoltek"), and the lenders identified on the signature pages hereto (each, a
"Lender" and, collectively, the "Lenders").

                                   RECITALS
                                   --------

         1.       Zoltek and the Lenders are parties to a Loan and Warrant
                  Agreement, dated as of September 29, 2005, as amended by
                  that certain Amendment No. 1 to Loan and Warrant Agreement
                  and Registration Rights Agreement dated as of April 28, 2006
                  (as amended, the "September Purchase Agreement"), pursuant
                  to which Zoltek issued and sold to the Lenders an aggregate
                  of $60,000,000 of Notes and certain Warrants (each as
                  defined in the September Purchase Agreement). The Notes and
                  Warrants issued under the September Purchase Agreement are
                  referred to in this Amendment as the "September Notes" and
                  "September Warrants," respectively. Capitalized terms used
                  and not defined in this Amendment shall have the respective
                  meanings set forth in the September Purchase Agreement.

         2.       In connection with the September Purchase Agreement, Zoltek
                  and the Lenders entered into a Registration Rights
                  Agreement, dated as of September 29, 2005, as amended by
                  that certain Amendment No. 1 to Loan and Warrant Agreement
                  and Registration Rights Agreement dated as of April 28, 2006
                  (as amended, the "September Registration Rights Agreement"),
                  pursuant to which Zoltek undertook certain registration
                  obligations to the Lenders.

         3.       Zoltek and the Lenders now wish to further modify certain of
                  the terms of the September Purchase Agreement and the
                  September Registration Rights Agreement.

         NOW, THEREFORE, in consideration of the foregoing Recitals and other
good and valuable consideration, the receipt and sufficiency of which are
hereby acknowledged, Zoltek and each Lender, severally and not jointly, agree
as follows:

1. Exercise of September Warrants. Subject to the terms hereof, each Lender
   ------------------------------
         agrees to exercise 100% of the warrants issued to the Lender in
         September 2005, December 2005 and February 2006 for an aggregate
         of 827,789 shares of Common Stock (pertaining to September Warrants
         to acquire an aggregate of 827,789 shares of Common Stock) on the
         Business Day following the date of this Agreement ("Closing Date").

         1.1 In consideration for such exercise, Zoltek shall issue to each
         Lender a warrant in the form of Exhibit B attached hereto (the
                                         ---------
         "Additional Warrants"), registered in the name





         of such Lender, pursuant to which such Lender shall have the right to
         acquire the number of shares of Common Stock indicated opposite such
         Lender's name on Schedule A hereto under the heading "Additional
                          ----------
         Warrants" at an Exercise Price of $28.06 per share.

2. Closing. Subject to the terms hereof and Section 7 and notwithstanding any
   -------
         provision of the September Purchase Agreement to the contrary, each
         Lender and Zoltek agree that the closing of the issuance of the
         Additional Warrants (the "Closing") shall occur on the Closing Date.

         2.1.     In connection with the Closing, Zoltek shall issue to each
                  Lender a warrant in the form of Exhibit B hereto, registered
                                                  ---------
                  in the name of such Lender pursuant to which such Lender
                  shall have the right to acquire the number of shares of
                  Common Stock indicated opposite such Lender's name on
                  Schedule A hereto under the heading "Additional Warrants."
                  ----------

         2.2.     The Additional Warrants will not be exercisable into shares
                  of Common Stock until the Company has obtained Nasdaq
                  Approval. For the purposes of this Amendment, the term
                  "Nasdaq Approval" shall mean the date in which the Company
                  receives approval from Nasdaq to issue all of the Additional
                  Warrants and the underlying shares of Common Stock
                  contemplated by this Amendment. Zoltek shall use its best
                  efforts to obtain the Nasdaq Approval as promptly as
                  possible. To the extent Nasdaq requires Zoltek to obtain the
                  consent of its shareholders, Zoltek hereby agrees that the
                  provisions of Section 11(iii) of the September Warrants
                  shall apply and are hereby incorporated into this Amendment.

3. Registration. Zoltek will use commercially reasonable efforts to prepare and
   ------------
         file a registration statement to cover all shares of Common Stock
         issuable under the Additional Warrants and the Registrable Securities
         issued to the Lenders in July 2006 and October 2006 pursuant to the
         September Loan Agreement (the "Additional Registration Statement").
         Such Additional Registration Statement shall constitute a
         "Registration Statement" under the September Registration Rights
         Agreement, and shall be subject to all the rights and obligations of
         and upon each of Zoltek and the "Lenders" thereunder. With respect to
         the Additional Registration Statement, as contemplated by Section
         2(b) of the September Registration Rights Agreement, the Filing Date
         shall be the 20th calendar day following the Closing Date. The
         calculation of the Effectiveness Date with respect to the Additional
         Registration Statement contemplated by Section 2(b) of the September
         Registration Rights Agreement shall be the earlier of: (i) the 90th
         day following the Closing Date; provided, however, that, if the
                                         --------  -------
         Commission reviews and has written comments to the filed Registration
         Statement that would require the filing of a pre-effective amendment
         thereto with the Commission, then the Effectiveness Date under this
         clause (i) shall be the 120th day following the date hereof and (ii)
         the fifth Trading Day following the date on which Zoltek is notified
         by the Commission that the initial Registration Statement will not be
         reviewed or is no longer subject to further review and comments.
         Notwithstanding any provision of Section 2(c) of the September
         Registration





         Rights Agreement to the contrary, in the event Zoltek breaches any of
         its obligations with respect to the Additional Registration Statement
         under this Section 3 or the September Registration Rights Agreement,
         Zoltek shall issue to the Lenders an amount of unregistered Common
         Stock equal to 35% of the total number of shares of Common Stock into
         which the New Warrants and the convertible notes and warrants
         originally issued to the Lenders in July 2006 and October 2006
         pursuant to the September Loan Agreement would be convertible or
         exercisable, as the case may be.

4. Certain Waivers.
   ---------------

         4.1.     In consideration of the transactions contemplated herein,
                  with respect to the inability of the Company to maintain the
                  availability of the Registration Statement on Form S-1 (the
                  "Resale Registration Statement") filed by the Company and
                  declared effective by the SEC with respect to registration
                  of the resale of Registrable Securities issued to the
                  Lenders in September 2005, December 2005, February 2006 and
                  May 2006 pursuant to the September Loan Agreement, and
                  Registrable Securities issued to the Lender pursuant to the
                  2003 Securities Purchase Agreement, the 2004 Securities
                  Purchase Agreement, the 2004 Loan Agreement and the 2005
                  Loan Agreement (the "Prior Transactions"), (i) the Lenders
                  hereby agree to waive and release Zoltek from any Event and
                  any liquidated or other damages to which the Lenders may be
                  entitled under the September Registration Rights Agreement
                  and the Prior Registration Rights Agreements or otherwise,
                  and (ii) the Lenders hereby waive any Event of Default
                  arising or continuing under all notes, debentures and
                  warrants issued pursuant to the September Purchase Agreement
                  and the Prior Transactions. For the purposes of this Section
                  4, the term "Prior Registration Rights Agreements" shall
                  mean each of the registration rights agreements among Zoltek
                  and the Lenders executed in connection with the Prior
                  Transactions. Notwithstanding the foregoing, in the event
                  that the foregoing Resale Registration Statement has not
                  been made available for use by the Lenders on or prior to
                  December 31, 2006, this waiver shall be null and void and
                  shall not be deemed to extend to any such failure and all
                  provisions of the September Registration Rights Agreement
                  and the Prior Registration Rights Agreements applicable with
                  respect to failure to maintain the availability of the
                  Resale Registration Statement for use by the Lenders shall
                  be reinstated.

         4.2.     In consideration of the transactions contemplated herein,
                  with respect to the fact that the Company did not file a
                  Registration Statement or have a Registration Statement
                  declared effective with respect to registration of the
                  resale of Registrable Securities issued to the Lenders
                  pursuant to the September Loan Agreement (i) the Lenders
                  hereby waive and release Zoltek from any Event and any
                  liquidated or other damages to which the Lenders may be
                  entitled under the September Registration Rights Agreement
                  or otherwise, and (ii) the Lenders hereby waive any Event of
                  Default arising or continuing under all notes, debentures
                  and warrants issued pursuant to the September Purchase
                  Agreement and the Prior Transactions. Notwithstanding the
                  foregoing, in the event that





                  Zoltek has not satisfied its obligations with respect to the
                  Additional Registration Statement under Section 3 above,
                  this waiver shall be null and void and shall not be deemed
                  to extend to any such failure and all provisions to maintain
                  the availability of the Resale Registration Statement for
                  use by the Lenders shall be reinstated.

         4.3.     In consideration of the transactions contemplated herein,
                  with respect to the delay by the Company in filing with the
                  SEC proxy materials calling a meeting of its shareholders
                  seeking approval of the Shareholder Proposal prior to the
                  Proxy Filing Date or obtain shareholder approval of the
                  Shareholder Proposal by the Shareholder Approval Date as
                  provided in Section 5(b)(iii) of the September Notes, the
                  Lenders hereby waive any Event of Default arising or
                  continuing under all notes, debentures and warrants issued
                  pursuant to the September Purchase Agreement and the Prior
                  Transactions. Notwithstanding the foregoing, in the event
                  that proxy materials calling a meeting of its shareholders
                  seeking approval of the Shareholder Proposal are not filed
                  prior to January 15, 2007, this waiver shall be null and
                  void and shall not be deemed to extend to any such failure
                  and all provisions of the September Purchase Agreement shall
                  be reinstated.

         4.4.     In consideration of the transactions contemplated herein,
                  the Lenders hereby amend the provisions of Section 4.16 and
                  any other provision of the September Purchase Agreement
                  which would prohibit or restrict the ability of Zoltek to
                  utilize the net proceeds from the sale of the securities
                  under the September Purchase Agreement to satisfy a
                  judgement, settle or post a bond with respect to the action
                  filed in the United States District Court for the Eastern
                  District of Missouri by SP Systems Inc. against a subsidiary
                  of Zoltek in an amount not to exceed $36,000,000.

5. Continued Validity of Transaction Documents under Purchase Agreements. The
   ---------------------------------------------------------------------
         parties hereto agree that the September Purchase Agreement, the
         September Registration Rights Agreement and the Transaction Documents
         entered into in connection therewith (as amended by this Amendment),
         remain in full force and effect, modified to the extent and only to
         the extent necessary to give effect to this Amendment and the
         transactions herein contemplated.

6. Miscellaneous.
   -------------

         6.1.     Fees and Expenses. Zoltek has agreed to reimburse Rockmore
                  -----------------
                  Investment Master Fund, Ltd ("Rockmore") $15,000 for its
                  legal fees and expenses in connection with this Amendment.
                  Accordingly, the amount Rockmore must pay to Zoltek upon
                  exercise of the warrants under Section 1 shall be reduced by
                  $15,000. Except for the foregoing, each party hereto will
                  bear the fees and expenses of its own counsel and advisors
                  in connection with the negotiation and entering into of this
                  Amendment. Zoltek shall pay all transfer agent fees, stamp
                  taxes and other taxes and duties levied in connection with
                  the issuance of any Securities.




         6.2.     Entire Agreement. This Amendment and the Transaction
                  ----------------
                  Documents, together with the exhibits and schedules thereto,
                  contain the entire understanding of the parties with respect
                  to the subject matter hereof and supersede all prior
                  agreements and understandings, oral or written, with respect
                  to such matters, which the parties acknowledge have been
                  merged into such documents, exhibits and schedules.

         6.3.     Equal Treatment of Lenders. No consideration shall be
                  --------------------------
                  offered or paid to any person to amend or consent to a
                  waiver or modification of any provision of any of the
                  Transaction Documents unless the same consideration is also
                  offered to all of the parties to the Transaction Documents.
                  For clarification purposes, this provision constitutes a
                  separate right granted to each Lender by Zoltek and
                  negotiated separately by each Lender, and is intended to
                  treat for Zoltek and the Lenders as a class and shall not in
                  any way be construed as the Lenders acting in concert or as
                  a group with respect to the purchase, disposition or voting
                  of Securities or otherwise.

         6.4.     Public Announcement. Zoltek shall, by 5:00 p.m. Eastern time
                  -------------------
                  on December 15, 2006, issue a press release disclosing the
                  material terms of the transactions contemplated hereby and
                  by 4:30 p.m. Eastern time on the second Business Day
                  following the date hereof, file a Current Report on Form
                  8-K, attaching such press release and the relevant
                  Transaction Documents thereto, each reasonably acceptable to
                  each Lender. Zoltek and each Lender shall consult with each
                  other in issuing any other press releases with respect to
                  the transactions contemplated hereby, and neither Zoltek nor
                  any Lender shall issue any such press release or otherwise
                  make any such public statement without the prior consent of
                  Zoltek, with respect to any press release of any Lender, or
                  without the prior consent of each Lender, with respect to
                  any press release of Zoltek, which consent shall not
                  unreasonably be withheld, except if such disclosure is
                  required by law, in which case the disclosing party shall
                  promptly provide the other party with prior notice of such
                  public statement or communication. Notwithstanding the
                  foregoing, Zoltek shall not publicly disclose the name of
                  any Lender, or include the name of any Lender in any filing
                  with the Commission or any regulatory agency or Trading
                  Market, without the prior written consent of such Lender,
                  except (i) as required by federal securities law in
                  connection with the registration statement contemplated by
                  the Registration Rights Agreement and (ii) to the extent
                  such disclosure is required by law or Trading Market
                  regulations, in which case Zoltek shall provide the Lenders
                  with prior notice of such disclosure permitted under
                  subclause (i) or (ii).

         6.5.     Notices. Any and all notices or other communications or
                  -------
                  deliveries required or permitted to be provided hereunder
                  shall be in writing and shall be deemed given and effective
                  as specified in the September Purchase Agreement. The
                  address for such notices and communications shall be as set
                  forth on the signature pages attached to the September
                  Purchase Agreement.




         6.6.     Amendments; Waivers. No provision of this Amendment may be
                  -------------------
                  waived or amended except in a written instrument signed, in
                  the case of an amendment, by Zoltek and each Lender or, in
                  the case of a waiver, by the party against whom enforcement
                  of any such waiver is sought. No waiver of any default with
                  respect to any provision, condition or requirement of this
                  Amendment shall be deemed to be a continuing waiver in the
                  future or a waiver of any subsequent default or a waiver of
                  any other provision, condition or requirement hereof, nor
                  shall any delay or omission of either party to exercise any
                  right hereunder in any manner impair the exercise of any
                  such right.

         6.7.     Amendment Controls. If any topic is addressed in the
                  ------------------
                  September Purchase Agreement and the September Registration
                  Rights Agreement (or any document related thereto), on the
                  one hand, and in this Amendment, on the other hand, this
                  Amendment shall control.

         6.8.     Construction. The headings herein are for convenience only,
                  ------------
                  do not constitute a part of this Amendment and shall not be
                  deemed to limit or affect any of the provisions hereof. The
                  language used in this Amendment will be deemed to be the
                  language chosen by the parties to express their mutual
                  intent, and no rules of strict construction will be applied
                  against any party.

         6.9.     Governing Law. All questions concerning the construction,
                  -------------
                  validity, enforcement and interpretation of this Amendment
                  shall be governed by and construed and enforced in
                  accordance with the internal laws of the State of New York,
                  without regard to the principles of conflicts of law
                  thereof. The parties agree that Section 8.8 of the September
                  Purchase Agreement shall apply to this Amendment as if set
                  forth in its entirety herein.

         6.10.    Survival. The representations and warranties contained
                  --------
                  herein shall survive the delivery, exercise and/or
                  conversion of the Securities, as applicable for the
                  applicable statue of limitations.

         6.11.    Execution. This Amendment may be executed in two or more
                  ---------
                  counterparts, all of which when taken together shall be
                  considered one and the same document and shall become
                  effective when counterparts have been signed by each party
                  and delivered to the other party, it being understood that
                  both parties need not sign the same counterpart.

         6.12.    Severability. If any provision of this Amendment is held to
                  ------------
                  be invalid or unenforceable in any respect, the validity and
                  enforceability of the remaining terms and provisions of this
                  Amendment shall not in any way be affected or impaired
                  thereby and the parties will attempt to agree upon a valid
                  and enforceable provision that is a reasonable substitute
                  therefor, and upon so agreeing, shall incorporate such
                  substitute provision in this Amendment.

         6.13.    Independent Nature of Lenders' Obligations and Rights. The
                  -----------------------------------------------------
                  obligations of each Lender hereunder are several and not
                  joint with the obligations of any other





                  Lender, and no Lender shall be responsible in any way for
                  the performance of the obligations of any other Lender.
                  Nothing contained herein, and no action taken by any Lender
                  pursuant hereto, shall be deemed to constitute the Lenders
                  as a partnership, an association, a joint venture or any
                  other kind of entity, or create a presumption that the
                  Lenders are in any way acting in concert or as a group with
                  respect to such obligations or the transactions contemplated
                  hereby. Each Lender shall be entitled to independently
                  protect and enforce its rights, including, without
                  limitation, the rights arising out of this Amendment and it
                  shall not be necessary for any other Lender to be joined as
                  an additional party in any proceeding for such purpose. The
                  Lenders have not relied upon the same legal counsel in their
                  review and negotiation of this Amendment. Zoltek has elected
                  to provide all Lenders with the same terms and form of
                  Amendment for the convenience of Zoltek and not because it
                  was required or requested to do so by the Lenders. Each
                  Lender represents that it has been represented by its own
                  separate legal counsel in its review and negotiations of
                  this Amendment and each party represents and confirms that
                  Malhotra & Associates LLP represents only Rockmore in
                  connection with this Amendment.

                           (Signature Pages Follow)









         IN WITNESS WHEREOF, the parties hereto have caused this Amendment to
be duly executed by their respective authorized signatories as of the date
first indicated above.

ZOLTEK COMPANIES, INC.



By: /s/ Kevin Schott
   ---------------------------------------------
   Name:  Kevin Schott
   Title: Chief Financial Officer

                  [REMAINDER OF PAGE INTENTIONALLY LEFT BLANK
                    SIGNATURE PAGE FOR PURCHASERS FOLLOWS]












         IN WITNESS WHEREOF, the undersigned have caused this Amendment to be
duly executed by their respective authorized signatories as of the date first
indicated above.

Name of Investing Entity: ______Omicron Master Trust
Signature of Authorized Signatory of Investing Entity: _________________________
Name of Authorized Signatory: __________________________________________________
Title of Authorized Signatory: _________________________________________________
Email Address of Authorized Entity:_____________________________________________









SCHEDULE A
- ----------

                      ---------------------------------------
                                                ADDITIONAL
                                                 WARRANTS
                      ---------------------------------------
                            Rockmore
                           Investment
                        Master Fund, Ltd         144,219
                      ---------------------------------------
                        Omicron Master
                            Trust                311,065
                      ---------------------------------------
                          Smithfield
                         Fiduciary LLC           124,168
                      ---------------------------------------
                        Iroquois Capital,
                              L.P.                82,779
                      ---------------------------------------
                       Cranshire Capital,
                              L.P.                82,779
                      ---------------------------------------
                           Midsummer
                        Investment Ltd.           82,779
                      ---------------------------------------
                              Total              827,789
                      ---------------------------------------