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                                                                     Exhibit 9.1



                             SHAREHOLDERS AGREEMENT

         THIS AGREEMENT is entered into as of this 12th day of May, 2000, by and
between VISTAGREEN HOLDINGS (BAHAMAS), LTD., a Bahamas international business
company ("Vistagreen"), MORAINE INVESTMENTS, INC., a British Virgin Islands
international business corporation ("Moraine"), and PARADISE STREAM (BAHAMAS)
LIMITED ("Paradise Stream"), a Bahamas international business company, each
having an address c/o Karp & Genauer, P.A., 2 Alhambra Plaza, Suite 1202, Coral
Gables, FL 33134, Attention: Joel J. Karp (Vistagreen, Moraine and Paradise
Stream are hereinafter collectively referred to as the "Vistagreen Parties"),
and the persons and entities listed on EXHIBIT "A" attached hereto, each having
an address c/o Terremark Holdings, Inc., 2601 South Bayshore Drive, PH 1-B,
Coconut Grove, Florida 33133, Attention: Brian Goodkind (collectively, the
"Terremark Shareholders").

                              W I T N E S S E T H :

         WHEREAS, Terremark Holdings, Inc., a Florida corporation ("Terremark")
and AmTec, Inc., a Delaware corporation ("AmTec") entered into the Agreement and
Plan of Merger dated as of November 24, 1999 ("Merger Agreement") pursuant to
which Terremark will merge into AmTec and the Terremark Shareholders will
receive shares of common stock of AmTec, $0.001 par value ("AmTec Common Stock")
as provided in the Merger Agreement; and

         WHEREAS, Vistagreen and AmTec entered into the Stock Purchase Agreement
dated as of November 24, 1999 ("Stock Purchase Agreement") pursuant to which,
immediately following the closing of the Merger Agreement, AmTec will sell to
the Vistagreen Parties or their assignees shares of AmTec Common Stock as
provided in the Stock Purchase Agreement in exchange for Note Proceeds (as
defined in the Stock Purchase Agreement), together with all interest earned
thereon; and

         WHEREAS, immediately following the closing of the Merger Agreement and
the closing of the Stock Purchase Agreement the percentage ownership of the
existing holders of AmTec Common Stock and Preferred Stock, Warrants, Options
and other securities upon total exercise




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or conversion prior to such closings shall be 25%, the percentage ownership of
the Vistagreen Parties shall be 35% and the percentage ownership of the
Terremark Shareholders shall be 40%, each such percentage representing the
respective ownership of such parties of the AmTec Common Stock on a fully
diluted basis immediately following such closings; and

         WHEREAS, certain affiliates of the Vistagreen Parties and certain
affiliates of Terremark entered into the Contract for the Purchase and Sale of
the General and Limited Partnership Interests of Terremark Centre, Ltd. dated as
of November 24, 1999 ("Terremark Centre Purchase Agreement"), which requires,
among other things, that the parties hereto enter into this Shareholders
Agreement with respect to certain matters relating to their ownership and voting
of AmTec Common Stock following the closings of the Merger Agreement and the
Stock Purchase Agreement.

         WHEREAS, the parties intend by entering into this Shareholders
Agreement ("Shareholders Agreement") to supercede by this Shareholders Agreement
all prior agreements with respect to the subject matter hereof; and

         NOW THEREFORE, in order to satisfy the above described requirements
contained in the Terremark Centre Purchase Agreement and in consideration of the
premises and for other good and valuable consideration, the receipt and
sufficiency of which is hereby acknowledged, the parties hereto agree as
follows:

         1. GENERAL AND DEFINITIONS. The recitals hereto are true and correct
and are hereby incorporated herein by this reference. For purposes of this
Agreement, a "Terremark Shareholder" shall include the persons and entities
listed on EXHIBIT "A" attached hereto and any Affiliate of any such persons or
entities. For purposes hereof, the "Vistagreen Parties" shall mean Vistagreen,
Paradise Stream and Moraine and any Affiliate of Vistagreen, Paradise Stream or
Moraine. For purposes hereof, "Affiliate" shall mean any person or entity that
directly or indirectly, through one or more intermediaries, controls, or is
controlled by, or is under common control with, such person or entity, and, in
the case of natural persons, shall also include any Family Member of any such
natural person, but only with regard to AmTec Common Stock received by such
Family Member from a party which acquired the same pursuant to the Merger
Agreement or the Stock Purchase Agreement. For purposes hereof, "Family Member"
of a natural person shall include the




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following relationships to such natural person: father, mother, son, daughter,
adopted son, adopted daughter, brother, sister, aunt, uncle, nephew, niece,
grandfather, grandmother and first cousin. For purposes hereof, "Vistagreen
Nominees" shall mean those persons designated by the Vistagreen Parties to serve
as members of the Board of Directors of AmTec. For purposes hereof, "Terremark
Nominees" shall mean those persons designated by the Terremark Shareholders to
serve as members of the Board of Directors of AmTec.

         2. ELECTION OF DIRECTORS. In connection with any and all elections of
Directors to the Board of Directors of AmTec, the Terremark Shareholders agree
to nominate or to cause to be nominated and to vote all of their shares of AmTec
Common Stock to elect two (2) Vistagreen Nominees to the Board of Directors of
AmTec. In addition, in connection with the election or appointment of members of
the Executive Committee of the Board of Directors of AmTec, the Terremark
Shareholders agree to elect or appoint or to cause all Terremark Nominees who
become Directors of AmTec to elect or appoint one (1) of the Vistagreen Nominees
to be a member of such Executive Committee. The Vistagreen Nominees shall advise
the Terremark Nominees regarding which of the Vistagreen Nominees shall be a
member of such Executive Committee. In connection with any and all elections of
Directors to the Board of Directors of AmTec, the Vistagreen Parties agree to
vote all of their shares of AmTec Common Stock in favor of electing all
Terremark Nominees who are nominated for directorships in connection with such
elections. In addition, in connection with the election or appointment of
members of any committee of the Board of Directors of AmTec, the Vistagreen
Parties agree to elect or appoint or to cause the Vistagreen Nominees who serve
as members of the Board of Directors of AmTec to elect or appoint such
Vistagreen Nominees as the Terremark Shareholders shall designate to be members
of such committees of the Board of Directors of AmTec as the Terremark
Shareholders shall designate.

         3.       TAGALONG RIGHTS.

                  (a) If any of the Vistagreen Parties or the Terremark
Shareholders propose to





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sell, dispose of or otherwise transfer any AmTec Common Stock (each a "Disposing
Stockholder"), such Disposing Stockholder shall refrain from effecting such
transaction unless, prior to the consummation thereof, each other stockholder of
AmTec who is a Vistagreen Party or a Terremark Stockholder (each a "Nondisposing
Stockholder") shall have been afforded the opportunity to join in such sale on a
pro-rata basis, as hereinafter provided, but subject to the limitations
hereinafter provided.

                  (b) Prior to consummation of any proposed sale, disposition or
transfer of AmTec Common Stock described in subparagraph (a) above, the
Disposing Stockholder shall cause the person or entity that proposes to acquire
such shares (the "Proposed Purchaser") to offer ("Purchase Offer") in writing to
each Nondisposing Stockholder to purchase shares of AmTec Common Stock owned by
such Nondisposing Shareholder, such that the number of shares of such AmTec
Common Stock so offered to be purchased from such Nondisposing Shareholder shall
be equal to the product obtained by multiplying the total number of shares of
such AmTec Common Stock then owned by such Nondisposing Shareholder, computed on
a fully diluted basis, by a fraction, the numerator of which is the aggregate
number of shares of AmTec Common Stock proposed to be purchased by the Proposed
Purchaser from all stockholders of AmTec (including all Disposing Stockholders)
and the denominator of which is the aggregate number of shares of AmTec Common
Stock then outstanding, computed on a fully diluted basis. Such purchase shall
be made at the highest price per share of AmTec Common Stock and on such other
terms and conditions as the Proposed Purchaser has offered to purchase shares of
AmTec Common Stock to be sold by the Disposing Stockholder. Each Nondisposing
Stockholder shall have twenty (20) days from the date of receipt of the Purchase
Offer in which to accept such Purchase Offer, and the closing of such purchase
shall occur simultaneously with the closing of the purchase of AmTec Common
Stock by the Proposed Purchaser from the Disposing Stockholder. The number of
shares of Common Stock to be sold to the Proposed Purchaser by the Disposing
Stockholder shall be reduced by the aggregate number of shares of Common Stock
purchased by the Proposed Purchaser from the Nondisposing Stockholders pursuant
to the acceptance by them of the Purchase Offer in accordance with the
provisions of





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this subparagraph (b), unless the Proposed Purchase is willing to purchase all
of the available shares of AmTec Common Stock of the Disposing Stockholder and
the Nondisposing Stockholders. In the event that a sale or other transfer
subject to this Section is to be made to a Proposed Purchaser, the Disposing
Stockholder shall notify the Proposed Purchaser that the sale or other transfer
is subject to this Section and shall insure that no sale or other transfer is
consummated without the Proposed Purchaser first complying with this Section. It
shall be the responsibility of each Disposing Stockholder to determine whether
any transaction to which it is a party is subject to this Section.

                  (c) Notwithstanding the foregoing, a Disposing Stockholder
shall not be subject to the restrictions of this Section in the event that the
Disposing Stockholder proposes to sell in any transaction or series of related
transactions a number of shares of AmTec Common Stock representing less than ten
percent (10%) of the issued and outstanding shares of Common Stock of AmTec. For
purposes of calculating the number of shares of AmTec Common Stock being sold in
any transaction or series of related transactions the shares being sold by all
Terremark Stockholders shall be aggregated as if being sold by one such
Stockholder and a similar aggregation shall apply to the Vistagreen Parties. In
addition, a Disposing Stockholder shall not be subject to the restrictions of
this Section in the event that a Disposing Stockholder proposes to sell shares
of AmTec Common Stock to an Affiliate of such Disposing Stockholder.

                  (d) The requirements of this paragraph 3 shall not apply to
open market sales through the American or other applicable Stock Exchange in
accordance with the rules of said Exchange (or the NASDAQ or any other
interdealer sale system in accordance with the rules of that system).
Notwithstanding the foregoing, the requirements of this paragraph shall apply to
any transaction involving direct negotiation between a buyer and a seller. For
this purpose, a registered broker dealer acting in the ordinary course of
business as a dealer, shall be deemed an intermediary, rather than a buyer.

         4. (a) Neither a Vistagreen Party nor a Terremark Shareholder may sell,
transfer,





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assign or otherwise dispose of any of its AmTec Common Stock to an Affiliate
unless such Affiliate agrees in writing to acquire such shares of AmTec Common
Stock subject to the terms of this Agreement and to be bound by the terms of
this Agreement. Any party who is not an Affiliate of a Vistagreen Party or a
Terremark Shareholder may acquire shares of AmTec Common Stock from a Vistagreen
Party or a Terremark Shareholder without being subject to the terms of this
Agreement, provided that the transaction pursuant to which such non-Affiliate
acquired such shares of AmTec Common Stock was not in violation of the terms of
this Agreement.

                  (b) The foregoing restriction shall not apply to open market
sales through the American or other applicable Stock Exchange in accordance with
the rules of said Exchange (or the NASDAQ or any other interdealer sales system
in accordance with the rules of that system). Notwithstanding the foregoing, the
foregoing restriction shall apply to any transaction involving direct
negotiation between a buyer and a seller. For this purpose a registered broker
dealer acting in the ordinary course of business as a dealer shall be deemed an
intermediary, rather than a buyer.

         5. This Agreement shall be binding on and inure to the benefit of the
respective parties hereto and their successors and assigns. This Agreement may
be executed in counterparts, each of which shall be deemed an original, but all
of which together shall constitute one and the same instrument. This Agreement
represents the entire understanding of the parties regarding the subject matter
hereof, and supersedes any and all other inconsistent or conflicting prior
agreements between the parties. The terms and provisions of this Agreement
cannot be terminated or modified or amended orally or by course of conduct or
dealing or in any manner except in a writing that is signed by the party against
whom enforcement is sought. This Agreement shall be construed in accordance with
the laws of the State of Florida, and any suit, action or proceeding arising out
of or relating to this Agreement may be commenced and maintained in any court of
competent subject matter jurisdiction in Miami-Dade County, Florida, and each
party waives objection to such jurisdiction and venue. The provisions of this
Agreement are severable, and any invalidity, unenforceability or illegality in
any provision or






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provisions hereof shall not affect the remaining provisions of this Agreement.
In any suit, action or proceeding arising out of or in connection with this
Agreement, the prevailing party shall be entitled to an award of the reasonable
attorneys' fees and disbursements incurred by such party in connection
therewith, including fees and disbursements in administrative, regulatory,
insolvency, bankruptcy and appellate proceedings. All notices required or
allowed hereunder shall be in writing and shall be deemed given upon (i) hand
delivery or (ii) delivery by reputable overnight courier service, or (iii)
delivery by facsimile with confirmation of receipt, or (iv) deposit of same in
the United States Certified Mail, Return Receipt Requested, first class postage
and registration fees prepaid and correctly addressed to the party for whom
intended at their address written in the first page hereof, or such other
address as is most recently noticed for such party as aforesaid. All references
to gender or number in this Agreement shall be deemed interchangeably to have a
masculine, feminine, neuter, singular or plural meaning, as the sense of the
context requires. This Agreement may be executed in counterparts all of which
shall constitute one and the same instrument.



         IN WITNESS WHEREOF, Purchaser and Sellers have executed this Contract
on the day and year first written above.


                                      VISTAGREEN HOLDINGS (BAHAMAS), LTD.



                                      By: /s/ ROGER CARPENTER
                                          -----------------------------------
                                              ROGER CARPENTER


                                      MORAINE INVESTMENTS, INC.

                                      By: /s/ ADRIAN CROSBIE-JONES
                                          -----------------------------------
                                              ADRIAN CROSBIE-JONES


                                      PARADISE STREAM (BAHAMAS) LIMITED)


                                      By: /s/ ADRIAN CROSBIE-JONES
                                          -----------------------------------
                                           ADRIAN CROSBIE-JONES, VICE PRESIDENT

                                      TERREMARK SHAREHOLDERS


                                      /s/ BRIAN GOODKIND
                                      ---------------------------------------
                                      BRIAN GOODKIND


                                      /s/ MICHAEL L. KATZ
                                      ---------------------------------------
                                      MICHAEL L. KATZ


                                      /s/ WILLIAM BIONDI
                                      ---------------------------------------
                                      WILLIAM BIONDI


                                      /s/ EDWARD P. JACOBSEN
                                      ---------------------------------------
                                      EDWARD P. JACOBSEN







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                                         /s/ IRVING I. PADRON, JR.
                                         ---------------------------------------
                                         IRVING I. PADRON, JR.


                                         /s/ AVIVA BUDD
                                         ---------------------------------------
                                         AVIVA BUDD



                                         TCO COMPANY, LTD.



                                         By: /s/ ADRIAN CROSBIE-JONES
                                             -----------------------------------

                                            Name:  ADRIAN CROSBIE-JONES
                                            Title: BUSINESS ADMINISTRATION
                                                   LIMITED-DIRECTOR


                                         /s/ MANUEL D. MEDINA
                                         ---------------------------------------
                                         MANUEL D. MEDINA


                                         /s/ WILLIAM BURMAYO
                                         ---------------------------------------
                                         WILLIAM BURMAYO


                                         ATTU SERVICES, INC.


                                         By: BUSINESS ADMINISTRATION LIMITED

                                         By:
                                             -----------------------------------
                                             ADRIAN CROSBIE-JONES, DIRECTOR


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                                   EXHIBIT "A"



                                 BRIAN GOODKIND

                                MICHAEL L. KATZ

                                 WILLIAM BIONDI

                               EDWARD P. JACOBSEN

                             IRVING I. PADRON, JR.

                                   AVIVA BUDD

                              TCO COMPANY LIMITED

                                MANUEL D. MEDINA

                                 WILLY BERMELLO

                              ATTU SERVICES, INC.