Document:

Exhibit 10.5

                            SHARE PURCHASE AGREEMENT

                 (Relating to Ordinary Shares of Gentium S.p.A.)

     THIS SHARE PURCHASE AGREEMENT, dated as of April 4, 2005 (this
"Agreement"), by and between FINSIRTON S.P.A., a corporation incorporated under
the laws of Italy (the "Seller"), and SIGMA TAU FINANZIARIA S.P.A., a
corporation incorporated under the laws of Italy (the "Buyer").

                              W I T N E S S E T H:

     WHEREAS, the Seller is the record and beneficial owner and registered
holder of 4,550,000 outstanding ordinary shares, par value (euro)1 ("Ordinary
Shares"), of Gentium S.p.A., a corporation incorporated under the laws of Italy
(the "Company"); and

     WHEREAS, upon the terms and subject to the conditions of this Agreement the
Seller wishes to transfer and sell to the Buyer, and the Buyer wishes to
purchase from the Seller, up to 940,000 Ordinary Shares and such Repricing
Shares (as defined below) as may become transferable to the Buyer pursuant to
Section 1.7;

     NOW, THEREFORE, in consideration of the premises and the mutual covenants
contained herein and other good and valuable consideration, the receipt and
sufficiency of which are hereby acknowledged, the parties hereto hereby agree as
follows:

                                   ARTICLE I

                           SALE AND PURCHASE OF SHARES

     1.1. Initial Sale of Shares. Upon the terms and subject to the conditions
of this Agreement, the Seller hereby agrees to sell, assign and transfer to the
Buyer, and the Buyer hereby agrees to purchase from the Seller, 800,000 Ordinary
Shares (the "Initial Shares") at $4.00 per share for an aggregate purchase price
of $3,200,000 (the "Aggregate Purchase Price").

     1.2. Second Sale of Shares. If the Company does not consummate an initial
public offering of its Ordinary Shares by May 31, 2005, the Buyer hereby agrees,
upon the request of the Seller, to purchase up to an additional 140,000 shares
(the "Secondary Shares" and, together with the Initial Shares, the "Shares")
from the Seller at $4.00 per share by June 30, 2005.

     1.3. Registration Rights. In connection with the sale of the Shares, the
Seller hereby agrees to cause the Company to register for resale under the
securities laws of the USA the Shares and any Repricing Shares (as defined
herein), if any, in accordance with the Investors' Rights Agreement in the form
attached hereto as Exhibit A.

     1.4. Initial Closing. The closing of the sale and purchase of the Initial
Shares hereunder (the "Initial Closing") shall take place within one business
day of the mutual execution of the Agreement (the date of such Initial Closing
being the "Initial Closing Date").

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     1.5. Second Closing. The closing of the sale and purchase of the Second
Shares hereunder, if any (the "Second Closing" and each of the Initial Closing
and the Second Closing being a "Closing") shall take place within three business
days of the Seller's request for such sale, and no later than June 30, 2005 (the
date of such Second Closing being the "Second Closing Date" and each of the
Initial Closing Date and the Second Closing Date being a "Closing Date").

     1.6. Closing Deliveries. At each Closing on the applicable Closing Date,
the Buyer shall wire immediately available funds for the purchase price of the
Shares in accordance with Seller's written instructions, and the Seller shall
deliver or cause to be delivered to Orrick, Herrington & Sutcliffe the
certificates for the Shares being sold and transferred by the Seller, duly
endorsed in favor of the Buyer or with appropriate share transfer powers in
favor of the Buyer, duly executed by the Seller, in proper form for transfer, in
the amount being sold by the Seller. The Seller shall cause Orrick, Herrington &
Sutcliffe to deliver the certificates for the Shares to Buyer within five (5)
business days following the receipt by the Seller of the purchase price for the
Shares. The Seller shall pay any and all transfer taxes which may be imposed
with respect to the delivery of the Shares. The parties shall execute and
deliver such other documents as may be required to validly transfer the Shares
to the Buyer and to enable the Buyer to become the registered holder thereof.

     1.7. Repricing Shares. In the event that the Company completes an initial
public offering or if the Company and its shareholders enter into an agreement
to sell all of the outstanding Ordinary Shares of the Company to a third party,
pursuant to which Ordinary Shares (the "Sale Shares") are issued or sold at a
price per share (the "Sale Share Price") less than $5.00 U.S. (such price
subject to equitable adjustments for share splits, share dividends,
combinations, recapitalizations, reclassifications and similar events occurring
after the Closing Date), the Buyer shall be entitled to receive from the Seller
an additional number of fully paid and nonassessable Ordinary Shares equal to
(x) the Aggregate Purchase Price divided by the product determined by
multiplying (i) 0.8 by (ii) the Sale Share Price less (y) the number of Shares
initially delivered to the Buyer on the Initial Closing Date and, if applicable,
the Second Closing Date pursuant to this Agreement (the "Repricing Shares"). If
the issuance would result in the issuance of a fraction of an Ordinary Share,
such fraction of an Ordinary Share shall be rounded down to the nearest whole
share. The Seller's obligation to deliver the certificates for Ordinary Shares
representing the Repricing Shares shall be absolute and unconditional,
irrespective of any action or inaction by the Buyer to enforce the same, any
waiver or consent with respect to any provision hereof, the recovery of any
judgment against any person or any action to enforce the same, any failure or
delay in the enforcement of any other obligation of the Seller to the Buyer, or
any setoff, counterclaim, recoupment, limitation or termination, or any breach
or alleged breach by the Buyer or any other person of any obligation to the
Seller or the Company or any violation or alleged violation of law by the Buyer
or any other person, and irrespective of any other circumstance which might
otherwise limit such obligation of the Seller to the Buyer in connection with
the issuance and delivery of the Repricing Shares. Such immediate and prompt
action shall be taken by all the parties in order to assure that there shall be
full compliance with the Seller's unqualified obligation that all Repricing
Shares to be delivered on or prior to the date the Company completes its initial
public offering or the date that the Company's shareholders sell of all of their
Ordinary

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Shares. The Seller shall pay any and all transfer taxes which may be imposed
with respect to the delivery of Repricing Shares.

                                   ARTICLE II

                  REPRESENTATIONS AND WARRANTIES OF THE SELLER

     The Seller represents and warrants to the Buyer as follows:

     2.1. Organization; Power and Authority. The Seller is a corporation duly
organized, validly existing and in good standing under the laws of the
jurisdiction of its formation and has all requisite corporate power and
authority to execute, deliver and perform its obligations hereunder, and to
consummate the transactions contemplated hereby.

     2.2. Authorization, Validity, Etc. of Shares. The Shares have been duly
authorized and validly issued and are fully paid and non-assessable. The Initial
Shares represent sixteen percent (16%) of the issued and outstanding Ordinary
Shares. The Second Shares represent two point eight percent (2.8%) of the issued
and outstanding Ordinary Shares.

     2.3. Title to Shares. The Seller has good and marketable title to the
Shares and the Repricing Shares, if any, free and clear of any and all liens,
pledges, charges, encumbrances, and claims and rights of others of any nature
whatsoever and, upon consummation of the sale and purchase of the Shares
pursuant to this Agreement, the Buyer will acquire good and marketable title to
the Shares and the Repricing Shares, if any, free and clear of any and all
liens, pledges, charges, encumbrances, and claims and rights of others of any
nature whatsoever.

     2.4. Authorization and Binding Effect. The execution, delivery and
performance of this Agreement by the Seller, and the consummation of the
transactions contemplated hereby on the part of the Seller, have been duly
authorized by all necessary action on the part of the Seller. This Agreement has
been duly executed and delivered by the Seller and constitutes the legal, valid
and binding obligation of the Seller, enforceable against the Seller in
accordance with its terms, except as may be limited by applicable bankruptcy,
reorganization, insolvency, moratorium or similar laws relating to or affecting
generally the enforcement of creditors' rights and except as the availability of
particular remedies of specific performance may be limited under generally
applicable rules of law, whether enforcement is sought at law or in equity.

     2.5. No Violation of Law or Other Agreements. The execution, delivery and
performance of this Agreement by the Seller, and the consummation of the
transactions contemplated hereby on the part of the Seller (a) do not conflict
with or constitute a violation of the organizational documents of the Seller;
(b) do not violate any material provision of applicable law or regulation or any
order, decree, judgment or award to which the Seller or any of its properties is
subject; and (c) do not and will not result in a breach of, or constitute a
default under, or constitute an event which, with notice or lapse of time, or
both, would become a default under, any indenture, loan agreement, credit
facility, material lease, or other material agreement or material instrument to
which the Seller is a party or by which the Seller or any of its properties is
bound. No authorization, approval or consent of, or notice to or filing with,
any person is or will be re-

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quired for the execution, delivery or performance of this Agreement by the
Seller or the consummation by the Seller of the transactions on its part
contemplated hereby.

     2.6. Information, Access, Etc. The Seller has requested and received from
the Company all information relating to the business, properties, operations,
condition (financial or other), results of operations, plans and prospects of
the Company deemed relevant by the Seller to its decision to sell the Shares and
Repricing Shares, if any; the Seller has been afforded the opportunity to ask
questions of the Company concerning the foregoing.

     2.7. Evaluation. In determining to enter into this Agreement and to sell
its Shares and Repricing Shares, if any, the Seller has relied upon the
information referred to in Section 2.6 and the Seller's own assessment of the
merits and risks of a sale of the Shares and Repricing Shares, if any, and has
not received or relied on any advice or evaluation by the Buyer.

     2.8. Litigation. There is no action, suit, or proceeding or investigation
pending or, to the knowledge of the Seller, currently threatened, in any such
case against the Seller or the Company or any of their respective directors,
officers, members or affiliates which questions the validity of this Agreement
or the right of the Seller to enter into this Agreement, to consummate the
transactions contemplated by this Agreement or to perform its obligations under
this Agreement, or which might result, either individually or in the aggregate,
in any material adverse change in the business, properties, operations,
condition (financial or other), results of operations, or prospects of the
Company. Neither the Seller nor the Company is a party or subject to the
provisions of any order, writ, injunction, judgment or decree of any court or
government agency or instrumentality. There is no action, suit, proceeding or
investigation by the Company currently pending or which the Company intends to
initiate.

     2.9. Approvals, Filings, Etc. No authorization, approval or consent of, or
filing with, any United States or foreign court, governmental body, regulatory
agency, self-regulatory organization, or arbitrator or any other person or
entity is required to be obtained or made by the Seller or the Company for the
execution, delivery and performance by the Seller and the Company of this
Agreement and the transactions contemplated by this Agreement.

     2.10. Organization of Company. The Company is a corporation duly organized,
validly existing and in good standing under the laws of Italy and has all
requisite corporate power and authority to own and lease its properties, to
carry on its business as presently conducted.

     2.11. Capitalization. The authorized capital shares of the Company consists
of 13,330,100 Ordinary Shares, of which 5,000,000 Ordinary Shares are issued and
outstanding. Except for (i) 2,216,100 shares which are reserved for issuance to
holders of the $8,010,000 aggregate principal amount of Series A Convertible
Notes issued by the Company and related warrants to purchase Ordinary Shares;
and (ii) 1,560,000 shares reserved for issuance under employee option plans, of
which 85,000 options have been granted, there are no outstanding securities of
the Company convertible into, exchangeable for, or otherwise entitling the
holder to acquire Ordinary Shares or other rights, agreements or arrangements of
any character under which the Company is or may be obligated to issue any
Ordinary Shares or other equity securities of any kind. Except for the Investor
Rights Agreement, the Investors' Rights Agreements between

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the Company and each of the holders of the Company's Series A Senior Convertible
Promissory Notes and related warrants and the Investors' Rights Agreement made
as of January 10, 2005 among the Company and the other parties thereto, the
Seller has no knowledge of any voting agreements, buy-sell agreements, option or
right of first purchase agreements or other agreements of any kind among any of
the security holders of the Company relating to the securities of the Company
held by them. Except for the Investors' Rights Agreement, the Investors' Rights
Agreements between the Company and each of the holders of the Company's Series A
Senior Convertible Promissory Notes and related warrants and the Investors'
Rights Agreement made as of January 10, 2005 among the Company and the other
parties thereto, the Company has not granted any person the right to require the
Company to register any securities of the Company under the Securities Act of
1933, as amended, whether on a demand basis or in connection with the
registration of securities of the Company for its own account or for the account
of any other person.

     2.12. No Related Agreements. The Seller has not, directly or indirectly,
entered into any agreement or understanding pursuant to which the Seller is
entitled to any rights, or subject to any obligations, with respect to the
Shares, including, without limitations, registration rights, rights of first
refusal, rights of first purchase, preemptive rights, tag along rights, drag
along rights, or voting rights.

                                  ARTICLE III

                   REPRESENTATIONS AND WARRANTIES OF THE BUYER

     The Buyer represents and warrants to the Seller as follows:

     3.1. Authorization and Binding Effect. This Agreement has been duly
executed and delivered by the Buyer, and this Agreement constitutes the legal,
valid and binding obligation of the Buyer, enforceable against such Buyer in
accordance with its terms, except as may be limited by applicable bankruptcy,
reorganization, insolvency, moratorium or similar laws relating to or affecting
generally the enforcement of creditors' rights and except as the availability of
particular remedies of specific performance may be limited under generally
applicable rules of law, whether enforcement is sought at law or in equity.

     3.2. Purchase for Investment; Circumstances of Offer. The Buyer is an
"accredited investor" as that term is defined in Rule 501 under the Securities
Act of 1933, as amended (the "1933 Act"), and, in particular, is a corporation
not formed for the specific purpose of acquiring the Shares or the Repricing
Shares and has total assets in excess of $5,000,000. The Buyer is purchasing the
Shares and Repricing Shares, if any, for its own account for investment and not
with a view towards the public sale or distribution thereof within the meaning
of the 1933 Act; and the Buyer has no intention of making any distribution,
within the meaning of the 1933 Act, of the Shares and Repricing Shares, if any,
except in compliance with the registration requirements of the 1933 Act or
pursuant to an exemption therefrom.

     3.3. Reoffers and Resales. The Buyer will not, directly or indirectly,
offer, sell, pledge, transfer or otherwise dispose of (or solicit any offers to
buy, purchase or otherwise acquire or take a pledge of) any of the Shares and
Repricing Shares, if any, unless registered un-

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der the 1933 Act and the rules and regulations promulgated thereunder or
pursuant to an exemption from registration under the 1933 Act.

     3.4. Information, Access, Etc. The Buyer has requested and received from
the Seller and the Company all information relating to the business, properties,
operations, condition (financial or other), results of operations or prospects
of the Company deemed relevant by the Buyer; and the Buyer has been afforded the
opportunity to ask questions of the Company concerning the foregoing.

     3.5. Evaluation. In determining to enter into this Agreement and to
purchase the Shares and Repricing Shares, if any, the Buyer has relied upon the
information referred to in Section 3.4 and the Buyer's own assessment of the
merits and risks of a purchase of the Shares and has not received or relied on
any advice or evaluation by the Seller.

     3.6. No Violation of Law or Other Agreements. The execution, delivery and
performance of this Agreement by the Buyer, and the consummation of the
transactions contemplated hereby on the part of the Buyer (a) do not conflict
with or constitute a violation of the organizational documents of the Buyer; (b)
do not violate any material provision of applicable law or regulation or any
order, decree, judgment or award to which the Buyer or any of its properties is
subject; and (c) do not and will not result in a breach of, or constitute a
default under, or constitute an event which, with notice or lapse of time, or
both, would become a default under, any indenture, loan agreement, credit
facility, material lease, or other material agreement or material instrument to
which the Buyer is a party or by which the Buyer or any of its properties is
bound. No authorization, approval or consent of, or notice to or filing with,
any person is or will be required for the execution, delivery or performance of
this Agreement by the Buyer or the consummation by the Buyer of the transactions
on its part contemplated hereby.

                                   ARTICLE IV

                CONDITIONS PRECEDENT TO OBLIGATIONS OF THE SELLER

     The obligation of the Seller to sell the Shares to the Buyer pursuant to
this Agreement is subject to the satisfaction of the following conditions at or
before the Closing (any or all of which may be waived by the Seller in its sole
discretion):

     4.1. Buyer's Performance. All of the covenants and agreements to be
complied with and performed by the Buyer on or before the Closing Date shall
have been complied with and performed in all material respects.

     4.2. Correctness of Buyer's Representations. All representations and
warranties of the Buyer contained in this Agreement shall be true and correct in
all material respects on and as of the Closing Date with the same force and
effect as if such representations and warranties had been made on and as of the
Closing Date.

     4.3. Investors' Rights Agreement. The Investors' Rights Agreement shall
have been executed and delivered by the parties thereto.

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<PAGE>

                                   ARTICLE V

                CONDITIONS PRECEDENT TO OBLIGATIONS OF THE BUYER

     The obligation of the Buyer to purchase the Shares pursuant to this
Agreement is subject to the satisfaction of the following conditions at or
before the Closing (any or all of which may be waived by the Buyer in its sole
discretion):

     5.1. Seller's Performance. All of the covenants and agreements to be
complied with and performed by the Seller on or before the Closing Date shall
have been complied with and performed in all material respects.

     5.2. Correctness of Seller's Representations. All representations and
warranties of the Seller contained in this Agreement and any other written
materials delivered to the Buyer shall be true and correct in all material
respects on and as of the Closing Date with the same force and effect as if such
representations and warranties had been made on and as of the Closing Date.

     5.3. Investors' Rights Agreement. The Investors' Rights Agreement shall
have been executed and delivered by the parties thereto.

     5.4. Issuer Acknowledgment and Agreement. The Issuer shall have
acknowledged the transfer of the Shares and Repricing Shares, if any, pursuant
to this Agreement and shall have agreed with the Buyer as set forth in the
Acknowledgement and Agreement appearing after the signatures of the parties to
this Agreement, all as evidenced by the execution and delivery to the Seller and
the Buyer of the Acknowledgement and Agreement in the form appearing after the
signatures of the parties to this Agreement.

                                   ARTICLE VI

                     CERTAIN COVENANTS; REPRESENTATIONS, ETC

     6.1. Best Efforts. The Seller and the Buyer shall use their best efforts to
cause the respective conditions to their obligations to close the transactions
contemplated hereby to be satisfied on or before the Closing Date. The Seller
and the Buyer agree to furnish a copy of this Agreement to the Company promptly
following execution and delivery hereof in order to obtain the confirmation by
the Company and the execution and delivery of instruments contemplated by this
Agreement.

     6.2. "Market Stand-Off" Agreement. The Buyer hereby agrees that, during a
period not to exceed one hundred and eighty (180) days (as determined by the
Company's Board of Directors and the proposed underwriters for a public offering
of the Company's securities under the 1933 Act), following the effective date of
a registration statement of the Company filed under the 1933 Act, it shall not,
to the extent requested in writing by the Company and such underwriter, sell or
otherwise transfer or dispose of (other than to donees who agree to be similarly
bound) any Ordinary Shares of the Company acquired hereunder held by it at any
time during such period except Ordinary Shares included in such registration and
to enter into a lock-up

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<PAGE>

agreement in usual and customary form with such underwriters providing that,
unless otherwise consented to by the managing underwriter, the holder of the
Shares will abide by the same restrictions as were approved by the Company's
Board of Directors; provided that, all officers and directors and greater than
one percent (1%) shareholders of the Company enter into similar agreements; and
provided further, however, that such lock up agreement shall not prohibit the
transfer of Repricing Shares, if any, from the Seller to the Buyer pursuant to
this Agreement. In order to enforce the foregoing covenants, the Company may
impose stop-transfer instructions with respect to the Shares, and Repricing
Shares, if any (and the shares or securities of every other person subject to
the foregoing restriction) until the end of such period.

     6.3. Capital Contribution to the Company. The Seller hereby agrees that
100% of the proceeds of the sale of the Shares (net of transfer taxes and the
fees payable to I-Bankers Securities) shall be irrevocably contributed to the
capital of the Company within one business day of the Closing Date, and that
Seller shall provide to Buyer copies of the documentation for such capital
contribution within five business days of the Closing Date.

     6.4. Board Nominee. The Seller hereby agrees to vote its Ordinary Shares in
favor of one nominee to the Company's Board of Directors selected by the Buyer.

                                  ARTICLE VII

                                     GENERAL

     7.1. Entire Agreement. This Agreement and the Investors' Rights Agreement
contains the entire agreement between the parties hereto with respect to the
subject matter hereof. This Agreement may not be amended, waived or modified
except by a writing signed by the party to be charged with enforcement.

     7.2. Binding Effect. This Agreement shall be binding upon and inure to the
benefit of the parties hereto and their respective successors and permitted
assigns; provided, however, this Agreement and all rights hereunder may not be
assigned by any party hereto without the prior written consent of the other
party hereto.

     7.3. Separate Counterparts. This Agreement may be executed in counterparts
and by the parties hereto on separate counterparts, each of which when so
executed shall constitute an original and all of which when taken together shall
constitute but one and the same instrument. A telephone line facsimile
transmission of this Agreement bearing a signature on behalf of a party hereto
shall be legal and binding on such party.

     7.4. Transaction Costs. Each party to this Agreement shall be responsible
for its own costs attendant to the transactions contemplated by this Agreement,
whether or not the Closing occurs.

     7.5. Cumulative Remedies. The remedies of the parties hereunder shall be
cumulative, and the exercise by the Seller of any of its remedies at law or in
equity to recover any damages shall not affect any other remedy available to the
Seller and the exercise by the

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Buyer of any of its remedies at law or in equity to recover any damages shall
not affect any other remedy available to the Buyer.

     7.6. Survival of Representations and Warranties. The respective
representations and warranties of the Seller and the Buyer set forth in this
Agreement shall survive the Closing notwithstanding any investigation made by or
on behalf of any such party.

     7.7. Notices. Except as otherwise expressly provided herein, all notices
hereunder, to be effective, shall be in writing and shall be mailed by certified
mail, postage and fees prepaid, or delivered personally or by telephone line
facsimile transmission to the party to be notified as follows:

If to the Seller:          FinSirton S.p.A.
                           Piazza XX Seppembre 2
                           22079 Villa Guardia (Como)
                           Italy
                           Facsimile No.:      011 39 031 385 241
                           Telephone No.:      011 39 030 385 217
                           Email:              scarsana@sirton.it

If to the Buyer:           Sigma Tau Finanziaria S.p.A.
                           Via Sudafrica 20
                           00144 Roma
                           Italy
                           United States of America
                           Facsimile No.:      011-39-06-542294-56
                           Telephone No:       011-39-06-542771-62
                           Email:              antonionicolai@sigma-tau.it

and shall be effective on receipt. A party may change the address to which such
communications are to be directed to it by giving written notice to the other
party hereto of such change in the manner above provided.

     7.8. Severability. The provisions of this Agreement are severable, and the
invalidity or unenforceability of any provision shall not affect the validity of
any other provision.

     7.9. No Waiver. The failure of a party at any time or times to require
performance of any provision hereof shall in any manner affect its right at a
later time to enforce the same. No waiver by a party of any condition, or of the
breach of any term, covenant, representation, warranty or agreement contained in
this Agreement, whether by conduct or otherwise, in any one or more instances
shall be deemed to be or construed as a further or continuing waiver of any such
condition or breach or a waiver of any other condition or of the breach of any
other term, covenant, representation, warranty or agreement contained in this
Agreement.

     7.10. Brokers, Finders, Etc. Each of the parties represents and warrants to
the other party that (except for I-Bankers Securities which has been retained by
the Seller and whose fees shall be payable solely by the Seller) it has not
retained or dealt with any person as broker,

                                      -9-
<PAGE>

finder or otherwise (each, a "Claimant") as would entitle any such person to any
fee or other compensation in connection with the transactions contemplated by
this Agreement and each of the parties agrees to indemnify and hold harmless the
other parties against any claim, cost or liability from any Claimant claiming by
or through the party giving such indemnity.

     7.11. Governing Law. Except for matters required under the laws of Italy
for the valid transfer of the Shares which shall be governed by the laws of
Italy, this Agreement shall be governed by and construed in accordance with the
laws of the internal laws of the State of New York.

     7.12. Jurisdiction. The parties hereby agree that all actions or
proceedings arising directly or indirectly from or in connection with this
Agreement shall be litigated only in the Supreme Court of the State of New York
or the United States District Court for the Southern District of New York
located in New York County, New York. The Seller consents and submits to the
jurisdiction and venue of the foregoing courts and consents that any process or
notice of motion or other application to either of said courts or a judge
thereof may be served on the Seller inside or outside the State of New York or
the Southern District of New York (but with respect to any party hereto, such
consent shall not be deemed a general consent to jurisdiction and service for
any third parties) by registered mail, return receipt requested, directed to the
Seller at its address provided in or pursuant to this Agreement (and service so
made shall be deemed complete three days after the same has been posted as
aforesaid) or by personal service or in such other manner as may be permissible
under the rules of said courts. The Seller hereby waives any right to object to
a proceeding in such courts based on inconvenience of the forum, waives any
right to a jury trial in connection with any litigation pursuant to this
Agreement and hereby waives, and agrees not to assert in any proceeding, any
claim that it is not personally subject to the jurisdiction of any such state or
federal court sitting in the City of New York. If either party shall commence a
proceeding to enforce any provision of this Agreement, then the prevailing party
shall be reimbursed by the other party for its attorney's fees and other costs
and expenses incurred with the investigation, preparation and prosecution of
such proceeding.

     7.13. Headings. The Article and Section headings, captions, headers and
footers contained in this Agreement are for convenience only and shall not form
part of or affect the interpretation of this Agreement.

     7.14. Further Assurances. Each party to this Agreement will perform any and
all acts and execute any and all documents as may be necessary and proper under
the circumstances in order to accomplish the intents and purposes of this
Agreement and to carry out its provisions.

     7.15. Certain Defined Terms. Capitalized terms defined in the introductory
paragraph of the recitals to this Agreement have the respective meaning in this
Agreement as so defined.

                            [Signature Page Follows]

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<PAGE>

     IN WITNESS WHEREOF, the parties hereto have duly executed this Agreement,
or caused this Agreement to be duly executed by their respective representatives
thereunto duly authorized, as of the date first above written.

                                  FINSIRTON S.P.A.

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

                                  SIGMA TAU FINANZIARIA S.P.A.

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

<PAGE>

                          ACKNOWLEDGEMENT AND AGREEMENT

     Gentium S.p.A., a corporation incorporated under the laws of Italy (the
"Company"), hereby:

          (1) consents to and acknowledges the transfer of the Shares and the
     Repricing Shares, if any, as provided in the foregoing Share Purchase
     Agreement (the "Agreement");

          (2) agrees that the Buyer shall have no liability or obligation, and
     the Company shall have no right or remedy against the Buyer, in respect of
     any breach or violation, or alleged breach or violation, by the Seller of
     any of its representations, warranties, obligations or agreements arising
     under or in connection with the any agreements between the Company and the
     Seller relating to the Shares or Repricing Shares, if any, or applicable
     law; and

          (3) acknowledges and agrees that the representations and warranties
     made by the Seller with respect to the Company in Article II of the
     Agreement are true and correct on the date hereof with the same force and
     effect as if such representations and warranties had been made by the
     Company on and as of the date hereof.

Capitalized terms used herein and not defined herein have the respective
meanings provided in the Agreement. By execution of this Acknowledgment and
Agreement, the Company does not become a party to the Agreement for any purpose
other than as expressly set forth in this Acknowledgement and Agreement. The
provisions of Article VII of the Agreement shall apply to this Acknowledgement
and Agreement and by this reference are incorporated herein as if set forth in
full at this place.

                                    GENTIUM S.P.A.

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

                                    Date:
                                         -------------------------------Exhibit 10.6

THE WARRANTS EVIDENCED BY THIS CERTIFICATE AND THE SECURITIES ISSUABLE UPON
EXERCISE HEREOF HAVE NOT BEEN REGISTERED UNDER THE SECURITIES ACT OF 1933, AS
AMENDED (THE "ACT"), OR ANY STATE SECURITIES LAWS AND NEITHER SUCH SECURITIES
NOR ANY INTEREST THEREIN MAY BE OFFERED, SOLD, PLEDGED, ASSIGNED OR OTHERWISE
TRANSFERRED UNLESS (1) A REGISTRATION STATEMENT WITH RESPECT THERETO IS
EFFECTIVE UNDER THE ACT AND ANY APPLICABLE STATE SECURITIES. LAWS, OR (2) ISSUER
RECEIVES AN OPINION OF COUNSEL TO THE HOLDER OF SUCH SECURITIES, WHICH COUNSEL
AND OPINION ARE REASONABLY SATISFACTORY TO ISSUER, THAT SUCH SECURITIES MAY BE
OFFERED, SOLD, PLEDGED, ASSIGNED OR TRANSFERRED IN THE MANNER CONTEMPLATED
WITHOUT AN EFFECTIVE REGISTRATION STATEMENT UNDER THE ACT OR APPLICABLE STATE
SECURITIES LAWS.

No. W-1                                                              Warrants
Issue Date: October 14, 2004                               New York, New York

                                 GENTIUM S.P.A.

                          WARRANT TO PURCHASE SHARES OF
                    COMMON STOCK, PAR VALUE (euro)1 PER SHARE

This Warrant Certificate certifies that, for value received, Defiance
Farmaceutica L.d.a. is the registered holder (the "Holder") of Warrants
("Warrants") to purchase, at any time commencing on the earlier to occur of (i)
the closing of a registered public offering on any of Nasdaq National or
SmallCap Market, the American Stock Exchange or the New York Stock Exchange (an
"Initial Public Offering") and (ii) the one year anniversary of the date hereof
as specified above (the "Issue Date"), subject to the terms and conditions
hereof, until 5:00 p.m., New York City time on the date that is the later of (w)
five (5) years and three (3) months after the Issue Date and (x) four (4) years
and three (3) months following the closing of the Initial Public Offering (the
"Expiration Date"), the number of shares of fully-paid and non-assessable shares
of common stock, (euro)1 par value per share (the "Common Stock"), of GENTIUM
S.P.A., a joint stock company (societa per azioni) incorporated and organized
under the laws of the Republic of Italy (the "Company"), equal to $660,000
divided by the lower of (i) ten dollars ($10.00) per share and (ii) the price
per share of Common Stock sold by the Company in an Initial Public Offering (but
not less than $6.00 per share) (in each case subject to adjustment as set forth
herein, the "Shares"). The per share exercise price for the shares of Common
Stock that may be purchased hereunder shall be one hundred ten percent (110%) of
the price per share of Common Stock sold by the Company in an Initial Public
Offering (but not less than $6.00 per share); provided, however, that if the
Company shall not have completed an Initial Public Offering on or prior to
October 14, 2005, the exercise price shall be six dollars ($6.00) per share
(such exercise price, as adjusted pursuant to the terms of this Warrant, the
"Exercise Price"). In order to exercise all or a part of this Warrant, the
Holder shall surrender this Warrant Certificate and pay the Exercise Price at
the principal office of the Company. Payment of the Exercise Price shall be made
by wire transfer or as otherwise provided in Section 1(b) or 1(f) hereof. The
Warrants represented by this Warrant Certificate is one of a series of similar
warrants (the "Investor Warrants") issued pursuant to those certain Subscription
Agreements, dated as of the date hereof, by and among the Company and the Holder
and the Company and certain other holders (each, a "Subscription Agreement" and
collectively, the "Subscription Agreements"). Capitalized terms used herein
without definition have the meanings ascribed to such terms in the Subscription
Agreements. The rights of the Holder of this Warrant Certificate shall be
subject to the following terms and conditions and to the text of the official
English translation of the resolution relating to the issuance of this Warrant
Certificate approved by the extraordinary shareholders' meeting of the Company
on September 30, 2004 as amended and supplemented by an additional extraordinary
shareholders' meeting of the Company on October 8, 2004 (the "Company
Resolution"), herewith enclosed as Exhibit A:

<PAGE>

     SECTION 1. Method of Exercise of Warrants; Exercise Price; Issuance of
Certificates.

     (a) The Holder of this Warrant Certificate may exercise the Warrants
evidenced hereby, in whole or in part, at any time, and from time to time, prior
to 5:00 p.m., New York City time, on the Expiration Date, by a duly executed
facsimile copy of the Election to Purchase attached hereto as Exhibit B, to the
Company at its principal office as set forth in the Investors' Rights Agreement.
Within ten (10) days from the delivery to the Company of the Election to
Purchase by facsimile copy, the Holder of this Warrant Certificate shall
surrender this Warrant Certificate by registered or certified mail, return
receipt requested, or by a nationally recognized overnight mail carrier, or by
hand delivery against written receipt thereof, together with payment of the
Exercise Price for each Share as to which the Warrants are exercised. Each
Warrant, to the extent not exercised prior to 5:00 p.m., New York City time, on
the Expiration Date shall become void and all rights thereunder shall cease as
of such time.

     (b) The aggregate Exercise Price shall be payable by wire transfer of
immediately available funds, by means of a cashless exercise pursuant to Section
1(f) hereof, or by any other means consented to by the Company.

     (c) Upon receipt of this Warrant Certificate representing exercisable
Warrants, with the Form of Election to Purchase attached hereto duly executed,
accompanied by payment of the aggregate Exercise Price for the Shares to be
purchased and an amount equal to any applicable transfer tax required to be paid
by the Holder in accordance with Section 6(c) hereof, the Company shall
thereupon promptly, and in no event later than five (5) business days
thereafter, cause to be issued to the Holder a certificate for the number of
whole shares of Common Stock so purchased.

     (d) If the Holder of this Warrant Certificate shall exercise less than all
the Warrants evidenced hereby, a new Warrant Certificate, substantially in the
form hereof, evidencing Warrants equivalent to the Warrants remaining
unexercised shall be issued by the Company to the Holder of this Warrant
Certificate or to its duly authorized assigns, subject to the provisions of
Section 5(a) hereof.

     (e) The Warrant Certificates and the certificates representing the shares
of Common Stock shall be executed on behalf of the Company in accordance with
the Company's Articles of Association. Warrant Certificates shall be dated the
date of execution by the Company upon initial issuance, division, exchange,
substitution or transfer. Each Warrant Certificate may be signed on behalf of
the Company by any person who, at the actual date of the execution of such
Warrant Certificate, shall be the proper officer of the Company to sign such
Warrant Certificate. If any officer whose signature is on a Warrant Certificate
no longer holds that office after the date of issuance of the Warrant
Certificate, such Warrant Certificate shall be valid nevertheless.

     (f) Notwithstanding any other provision in this Warrant to the contrary, if
on or prior to the one (1) year anniversary of the Initial Public Offering, the
Company has not yet filed with the Securities and Exchange Commission a
registration statement (the "Registration Statement") with respect to the resale
by the Holder of the Shares, or if a Registration Statement has been so filed
but is not effective at any time following the fourteen (14) month anniversary
of the Initial Public Offering, then for as long as no such Registration
Statement is effective with a current prospectus available, this Warrant may
also be exercised, in whole or in part, at any time prior to the Expiration
Date, by means of a "cashless exercise" in which the Holder shall be entitled to
receive a certificate for the number of Shares equal to the quotient obtained by
dividing [(A-B)(X)] by (A), where:

     (A)  = the closing bid price on the trading day preceding the date of such
          election;

     (B)  = the Exercise Price of the Warrants, as adjusted; and

                                      -2-
<PAGE>

     (X)  = the number of Shares issuable upon exercise of the Warrants in
          accordance with the terms of this Warrant.

     SECTION 2. Split Up, Combination and Exchange of Warrant Certificates;
Mutilated, Destroyed, Lost or Stolen Warrant Certificates; Warrant Register.

     (a) Subject to the provisions of Section 5(a) hereof, at or prior to the
Expiration Date, this Warrant Certificate, with or without other Warrant
Certificates, may be split up, combined or exchanged for another Warrant
Certificate or Warrant Certificates, entitling the Holder to purchase a like
number of shares of Common Stock as the Warrant Certificate or Warrant
Certificates surrendered then entitled the Holder to purchase. Any Holder
desiring to split up, combine or exchange this Warrant Certificate shall make
such request in writing delivered to the Company, and shall surrender the
Warrant Certificate or Warrant Certificates to be split up, combined or
exchanged at the office of the Company maintained for such purpose as set forth
below. Thereupon the Company shall sign and deliver to the person or entity
entitled thereto a Warrant Certificate or Warrant Certificates, as the case may
be, as so requested. TheCompany may require payment of a sum sufficient to cover
any transfer tax that may be imposed in connection with any split-up,
combination or exchange of Warrant Certificates.

     (b) Upon receipt by the Company of evidence reasonably satisfactory to it
of the loss, theft, destruction or mutilation of this Warrant Certificate, and,
in case of loss, theft or destruction, of indemnity or security reasonably
satisfactory to it and reimbursement to the Company of all reasonable expenses
incidental thereto, and upon surrender and cancellation of the Warrant
Certificate if mutilated, the Company will make and deliver a new Warrant
Certificate of like tenor to the Holder in lieu of the Warrant Certificate so
lost, stolen, destroyed or mutilated.

     (c) The Company will maintain at its principal office a Warrant register
upon which transfers and exchanges of Warrants shall be recorded. Such office is
currently located at Piazza XX Settembre, n.2, 22079, Villa Guardia, Como,
Italy.

     SECTION 3. Subsequent Issue of Warrant Certificates. Subsequent to their
original issuance, no Warrant Certificates shall be issued except (a) Warrant
Certificates issued upon any transfer, combination, split-up or exchange of
Warrants pursuant to the terms, conditions and provisions hereof, (b) Warrant
Certificates issued in replacement of mutilated, destroyed, lost or stolen
Warrant Certificates pursuant to Section 2 hereof and (c) Warrant Certificates
issued pursuant to Section l(d) hereof upon the partial exercise of any Warrant
Certificate to evidence the unexercised portion of such Warrant Certificate.

     SECTION 4. Cancellation and Destruction of Warrant Certificates. All
Warrant Certificates surrendered for the purpose of exercise, exchange,
substitution, transfer, split-up or combination shall be cancelled by the
Company, and no Warrant Certificates shall be issued in lieu thereof except as
expressly permitted by any of the provisions of this Warrant Certificate. The
Company shall cancel and retire any other Warrant Certificates purchased or
acquired by the Company otherwise than upon the exercise thereof.

     SECTION 5. Ownership; Restrictions on Transfer, Legends.

     (a) The Holder of this Warrant Certificate, by its acceptance hereof,
covenants and agrees that the Warrants evidenced hereby are being acquired as an
investment and not with a view to the distribution thereof and that the Warrants
may not be sold, transferred, assigned, hypothecated or otherwise disposed of in
any way, in whole or in part, except in compliance with the Securities Act of
1933, as amended (the "Act") and the provisions of this Warrant Certificate and
that certain Investors' Rights Agreement, dated as of

                                      -3-
<PAGE>

the date hereof, by and among the Company and the investors listed as parties
thereto (the "Investors' Rights Agreement"). To be effective under this Warrant
Certificate, any transfer, sale or other disposition of the Warrants shall be
registered with the Company by submission to it of this Warrant Certificate,
together with a notice of transfer in the form of the transfer form (the
"Transfer Form") attached hereto as Exhibit B, duly completed and executed, and
payment of any and all applicable taxes, expenses or charges in respect of such
transaction pursuant to Section 6(c) hereof. Within five business days after the
Company's receipt of the Warrant Certificate, the Transfer Form so completed and
executed and the payment of such taxes, expenses or charges, if any, the Company
will issue and deliver to the transferee a new Warrant Certificate representing
the portion of the Warrants transferred and otherwise having the same terms and
provisions as this Warrant Certificate, which the Company will register in the
new Holder's name. In the event of a partial transfer of the Warrants, the
Company shall concurrently issue and deliver to the transferring Holder -a new
Warrant Certificate that entitles the transferring Holder to the balance of the
Warrants' not so transferred and that otherwise is upon the same terms and
provisions as this Warrant Certificate. Upon the due delivery of this Warrant
Certificate for transfer, the transferee shall be deemed for all purposes to
have become the Holder of the new Warrant Certificate issued in respect of the
Warrants transferred, effective immediately prior to the close of business on
the date of such delivery, irrespective of the date of actual delivery of such
new Warrant Certificate representing such transferred Warrants.

     (b) Each Warrant Certificate (including each Warrant Certificate issued
upon the transfer of such Warrant Certificate) shall be stamped or otherwise
imprinted with a legend in substantially the form of the legend on the face
hereof.

     (c) The Warrants, and the shares of Common Stock issuable upon exercise of
the Warrants, have not been registered under the Act. Upon exercise, in part or
in whole, of the Warrants, certificates representing the shares of Common Stock
issuable upon exercise of the Warrants shall be stamped or otherwise imprinted
with a legend in substantially the following form:

     "THE SECURITIES REPRESENTED HEREBY HAVE NOT BEEN REGISTERED UNDER THE
     SECURITIES ACT OF 1933, AS AMENDED (THE "ACT"), OR ANY STATE SECURITIES
     LAWS AND NEITHER SUCH SECURITIES NOR ANY INTEREST THEREIN MAY BE OFFERED,
     SOLD, PLEDGED, ASSIGNED OR OTHERWISE TRANSFERRED UNLESS (1) A REGISTRATION
     STATEMENT WITH RESPECT THERETO IS EFFECTIVE UNDER THE ACT AND ANY
     APPLICABLE STATE SECURITIES LAWS, OR (2) ISSUER RECEIVES AN OPINION OF
     COUNSEL TO THE HOLDER OF SUCH SECURITIES, WHICH COUNSEL AND OPINION ARE
     REASONABLY SATISFACTORY TO ISSUER, THAT SUCH SECURITIES MAY BE OFFERED,
     SOLD, PLEDGED, ASSIGNED OR TRANSFERRED IN THE MANNER CONTEMPLATED WITHOUT
     AN EFFECTIVE REGISTRATION STATEMENT UNDER THE ACT OR APPLICABLE STATE
     SECURITIES LAWS.

     SECTION 6. Reservation and Availability of Shares of Common Stock; Taxes.

     (a) The Company shall at all times have authorized and reserved, free from
any preemptive or similar rights, and shall keep available out of its authorized
and unissued shares of Common Stock, the number of shares of Common Stock that
will be sufficient to permit the exercise in full of all outstanding Warrants
from time to time.

     (b) The Company shall take all such action as may be necessary to ensure
that all shares of Common Stock delivered upon exercise of Warrants shall, at
the time of delivery of the certificates for

                                      -4-
<PAGE>

such shares (subject to payment of the Exercise Price), be duly and validly
authorized and issued, fully paid and non-assessable, and free and clear of any
and all taxes, liens and charges with respect to the issuance thereof, and the
issuance of such shares of Common Stock shall not be subject to any preemptive
or similar right of the Company or any other person or entity (all of which
rights being hereby waived irrevocably).

     (c) The Company shall pay when due and payable any and all issue or other
taxes and charges that may be payable in respect of the initial issuance or
delivery of this Warrant Certificate or of the issuance or delivery of any
shares of Common Stock upon the exercise of Warrants, except as set forth in the
immediately following sentence. The Company shall not, however, be required to
pay any tax which may be payable in respect of any transfer involved in the
issue or delivery of this Warrant Certificate to a person or entity other than,
or the issuance or delivery of certificates for Common Stock in a name other
than that of, the Holder of the Warrant Certificate evidencing Warrants
surrendered for exercise or to issue or deliver any certificates for shares of
Common Stock upon the exercise of any Warrants until any such tax shall have
been paid (any such tax being payable by the Holder of such Warrant Certificate
at the time of surrender) or until it has been established to the Company's
satisfaction that no such tax is due.

     SECTION 7. Common Stock Record Date. Each person or entity in whose name
any certificate for shares of Common Stock is issued upon the exercise of
Warrants shall for all purposes be deemed to have become the holder of record of
the Common Stock represented thereby on, and such certificate shall be dated,
the close of business on the date upon which the Warrant Certificate evidencing
such Warrants was duly surrendered and payment of the Exercise Price (and any
applicable transfer taxes) was made; provided, however, that if the date of such
surrender and payment is a date upon which the Common Stock transfer books of
the Company are closed, such person or entity shall be deemed to have become the
record holder of such shares on, and such certificate shall be dated, the
opening of business on the next succeeding business day on which the Common
Stock transfer books of the Company are open.

     SECTION 8. Adjustments to Exercise Price, Number of Shares and Number of
Warrants.

     (a) Special Definitions. For purposes of this Section 8, the following
definitions apply:

     (1) "Options" shall mean rights, options, or warrants to subscribe for,
purchase or otherwise acquire either Common Stock or Convertible Securities
(defined below).

     (2) "Convertible Securities" shall mean any evidences of indebtedness,
shares (other than Common Stock) or other securities convertible into or
exchangeable for Common Stock.

     (3) "Additional Shares of Common Stock" shall mean all shares of Common
Stock issued (or pursuant to Section 8(c), deemed to be issued) by the Company
after the Issue Date, other than shares of Common Stock issued or issuable:

     (A) to officers, directors or employees of, or consultants to, the Company
pursuant to any compensation agreement, plan or arrangement or the issuance of
Common Stock upon the exercise of any such options or warrants;

     (B) upon conversion of existing convertible securities outstanding as of
the Issue Date;

                                      -5-
<PAGE>

     (C) upon exercise of outstanding warrants existing as of the Issue Date
(including, without limitation, the Investor Warrants);

     (D) to an institution or bank lender in connection with a loan transaction
or equipment lease;

     (E) to any persons or entities as consideration for an acquisition by the
Company of any entity or business, or other similar transaction; or

     (F) upon exercise of Investor Warrants or conversion of the Notes, in each
case whether or not existing as of the Issue Date.

     (b) No Adjustment of Exercise Price. Any provision herein to the contrary
notwithstanding, no adjustment in the Exercise Price shall be made in respect of
the issuance of Additional Shares of Common Stock unless the consideration per
share (determined pursuant to Section 8(e) hereof) for an Additional Share of
Common Stock issued or deemed to be issued by the Company is less than the
Exercise Price in effect on the date of, and immediately prior to such issue.

     (c) Deemed Issue of, Additional Shares of Common Stock. In the event the
Company at any time or from time to time after the Issue Date shall issue any
Options or Convertible Securities or shall fix a record date for the
determination of holders of any class of securities then entitled to receive any
such Options or Convertible Securities, then the maximum number of shares (as
set forth in the instrument relating thereto without regard to any provisions
contained therein designed to protect against dilution) of Common Stock issuable
upon the exercise of such Options or, in the case of Convertible Securities and
Options therefor, the conversion or exchange of such Convertible Securities,
shall be deemed to be Additional Shares of Common Stock issued as of the time of
such issue or, in case such a record date shall have been fixed, as of the close
of business on such record date, provided further that in any such case in which
Additional Shares of Common Stock are deemed to be issued:

     (1) no further adjustments in the Exercise Price shall be made upon the
subsequent issue of Convertible Securities or shares of Common Stock upon the
exercise of such Options or conversion or exchange of such Convertible
Securities;

     (2) if such Options or Convertible Securities by their terms provide, with
the passage of time or otherwise, for any increase in the consideration payable
to the Company, or decrease in the number of shares of Common Stock issuable,
upon the exercise, conversion or exchange thereof, the Exercise Price computed
upon the original issue thereof (or upon the occurrence of a record date with
respect thereto), and any subsequent adjustments based thereon, shall, upon any
such increase or decrease becoming effective, be recomputed to reflect such
increase or decrease insofar as it affects such Options or the rights of
conversion or exchange under such Convertible Securities;

     (3) no readjustment pursuant to clause (2) above shall have the effect of
increasing the Exercise Price to an amount which exceeds the lower of (A) the
Exercise Price on the original adjustment date, or (B) the Exercise Price that
would have resulted from any issuance of Additional Shares of Common Stock
between the original adjustment date and such readjustment date.

     (d) Adjustment of Exercise Price Upon Issuance of Additional Shares of
Common Stock. In the event the Company at any time after the Issue Date shall
issue Additional Shares of Common Stock (including Additional Shares of Common
Stock deemed to be issued pursuant to Section 8(c)) without consideration or for
a consideration per share less than the Exercise Price in effect on the date of
and immediately prior to such issue, then and in such event, the Exercise Price
shall be reduced, con-

                                      -6-
<PAGE>

currently with such issue, (x) if the issuance or deemed issuance occurs prior
to the completion of the Initial Public Offering, to a price (calculated to the
nearest cent) equal to the price per share received by the Company upon the
issuance of Additional Shares of Common Stock or (y) if the issuance occurs
following the completion of the Initial Public Offering, to a price (calculated
to the nearest cent) determined oby multiplying such Exercise Price by a
fraction, the numerator of which shall be the number of shares of Common Stock
outstanding immediately prior to such issue plus the number of shares of Common
Stock which the aggregate consideration received by the Company for the total
number of Additional Shares of Common Stock so issued would purchase at such
Exercise Price in effect immediately prior to such issuance, and the denominator
of which shall be the number of shares of Common Stock outstanding immediately
prior to such issue plus the number of such Additional Shares of Common Stock so
issued. For the purpose of the above calculation, the number of shares of Common
Stock outstanding immediately prior to such issue shall be calculated on a fully
diluted basis, as if all Convertible Securities had been fully converted into
shares of Common Stock and any outstanding warrants, options or other rights for
the purchase of shares of stock or convertible securities had been fully
exercised (and the resulting securities fully converted into shares of Common
Stock, if so convertible) as of such date.

     (e) Determination of Consideration. For purposes of this Section 8, the
consideration received by the Company for the issue of any Additional Shares of
Common Stock shall be computed as follows:

     (1) Cash and Property. Such consideration shall:

     (A) insofar as it consists of cash, be computed at the aggregate amount of
cash received by the Company excluding amounts paid or payable for accrued
interest or accrued dividends;

     (B) insofar as it consists of property other than cash, be computed at the
fair value thereof at the time of such issue, as determined in good faith by the
Board of Directors of the Company; and

     (C) in the event Additional Shares of Common Stock are issued together with
other shares or securities or other assets of the Company for consideration
which covers both, be the proportion of such consideration so received, computed
as provided in clauses (A) and (B) above, as determined in good faith by the
Board of Directors of the Company.

     (2) Options and Convertible Securities. The consideration per share
received by the Company for Additional Shares of Common Stock deemed to have
been issued pursuant to Section 8(c), relating to Options and Convertible
Securities shall be determined by dividing

     (A) the total amount, if any, received or receivable by the Company as
consideration for the issue of such Options or Convertible Securities, plus the
minimum aggregate amount of additional consideration (as set forth in the
instruments relating thereto, without regard to any provision contained therein
designed to protect against dilution) payable to the Company upon the exercise
of such Options or the conversion or exchange of such Convertible Securities, or
in the case of Options for Convertible Securities, the exercise of such Options
for Convertible Securities and the conversion or exchange of such Convertible
Securities by

     (B) the maximum number of shares of Common Stock (as set forth in the
instruments relating thereto, without regard to any provision contained therein
designed to protect against the dilution) issuable upon the exercise of such
Options or conversion or exchange of such Convertible Securities.

                                      -7-
<PAGE>

     SECTION 9. Elimination of Fractional Interests. The Company shall not be
required to issue certificates representing fractions of shares of Common Stock
upon the exercise of the Warrants, nor shall it be required to issue scrip or
pay cash in lieu of fractional interests, it being the intent of the parties
that all fractional interests shall be eliminated by rounding any fraction up to
the nearest whole number of shares of Common Stock, or other securities,
properties or rights.

     SECTION 10. Registrations; Listing of Securities. The Company covenants and
agrees that if any shares of capital stock to be reserved for the purpose of the
issuance of shares upon the exercise of the Warrants requires registration with
or approval of any governmental or other authority under any federal or state
law before such shares may be validly issued or delivered upon exercise, then
the Company will in good faith and as expeditiously as possible endeavor to
secure such registration or approval, as the case may be. If and so long as the
Common Stock issuable upon the exercise of the Warrants is listed on any
national securities exchange or automated quotation system, the Company will, if
permitted by the rules of such exchange or automated quotation system, as
applicable, list and keep listed on such exchange or automated quotation system,
as applicable, upon official notice of issuance, all shares of such Common Stock
issuable upon exercise of the Warrants.

     SECTION 11. Rights of Warrant Holder. If at any time prior to the
expiration of the warrants and their exercise any of the following actions,
activities, events, circumstances, conditions or transactions shall be proposed:

     (a) the Company shall issue (by distribution or otherwise) or sell or
transfer any Common Stock or any other capital stock of the Company or rights,
warrants or options or convertible, exercisable or exchangeable securities
containing the right to subscribe for, convert, exercise or exchange into or
purchase any additional shares of Common Stock or shares of any other capital
stock of the Company or any other securities, rights, warrants or options;

     (b) the Company shall effect any reorganization, recapitalization or
reclassification of its Common Stock or its other capital stock;

     (c) the Company shall effect any reorganization, consolidation, merger or
sale, transfer, lease or other disposition of all or substantially all of the
property, assets, stock or business of the Company;

     (d) the Company shall effect an initial public offering of Company Stock;

     (e) the Company shall apply any property or assets to the purchase,
acquisition, redemption or retirement of any of its Common Stock or its other
capital stock; or

     (f) the Company shall effect a dissolution, liquidation or winding up of
the Company,

then in any one or more of said events, the Company shall give written notice of
such event to the Holder at least thirty (30) days prior to the date fixed as a
record date or the date of closing the transfer books for the determination of
the stockholders entitled to any such asset or to vote on such proposed action,
activity, event, circumstance, condition or transaction, or the consummation of
such action, activity, event, circumstance, condition or transaction if no vote
of stockholders is required.

     SECTION 12. Limitation of Rights. No mere enumeration herein of the rights
or privileges of the Holder shall give rise to any rights or privileges of the
Holder as a stockholder of the Company solely by reason of its ownership of the
Warrants.

                                      -8-
<PAGE>

     SECTION 13. Notices. Except as otherwise expressly specified herein, all
notices, requests and other communications required or permitted hereunder shall
be in writing and shall be sent by an internationally recognized overnight
courier service; by certified or registered mail, return receipt requested (or,
in the case of a notice sent to an address in Italy, by international express
mail, return receipt requested); by facsimile transmission or by hand delivery.

                  to e Company:         Gentium S.p.A.
                                        Piazza XX Settembre, n.2
                                        22079 Villa Guardia Como
                                        Italy

                                        Attention: Dott. Sauro Carsana
                                        Fax:+39 031 385333

                  and, if to the Holder, to the name and address specified with
                  respect to such person or entity in the Warrant register
                  maintained by the Company pursuant to Section 2(c) hereof.

Any party may designate a different notice address, contact person, telephone
number or facsimile number with respect to such party by providing a notice
describing such changes to the other party hereto in accordance with the
provisions of this Section 13. Any notice sent by internationally recognized
overnight mail courier service shall be deemed to be delivered to the address
shown on the mailing receipt on the expected date of delivery upon proper
evidence of mailing for purposes of this Section 13. Any notice sent by
certified or registered mail, return receipt requested (or, in the case of a
notice sent to an address in Italy, by international express mail, return
receipt requested), shall be deemed to be delivered five business days after
mailing. Any notice sent by facsimile transmission shall be deemed delivered as
of the open of business on the business day following the date on which sent
provided the sender receives written confirmation of transmission and provided
that within 24 hours such notice is also sent by regular mail or by an
internationally-recognized overnight mail courier service to the appropriate
address specified above. Any notice sent by hand delivery shall be deemed
delivered as of the date of delivery.

     SECTION 14. Successors. This Warrant Certificate shall be binding upon and
inure to the benefit of the Company and the Holder and their respective
successors and permitted assigns; provided that the Company may not assign,
delegate or otherwise transfer any of its rights or obligations under this
Warrant Certificate without the written consent of the Holder. Holders may
assign its rights hereunder in the manner and to the persons permitted under the
Investors' Rights Agreement.

     SECTION 15. Governing Law: Submission to Jurisdiction.

     (a) This Warrant Certificate shall be construed in accordance with and
governed by the laws of the State of New York without regard to principles of
conflicts of laws, except for the application of the provisions of Italian law
concerning the proper authorization and issuance of warrant certificates.

     (b) In case of any inconsistencies between the text of this Warrant
Certificate and the text of the Company Resolution, the text of the Company
Resolution shall govern.

     (c) IN THE EVENT THAT A JUDICIAL PROCEEDING IS NECESSARY, THE EXCLUSIVE
FORUMS FOR. RESOLVING DISPUTES ARISING OUT OF OR RELATING TO THIS AGREEMENT ARE
EITHER THE SUPREME COURT OF THE STATE OF NEW YORK IN AND FOR THE COUNTY OF NEW
YORK OR THE FEDERAL COURTS FOR SUCH STATE AND COUNTY, AND ALL RELATED APPELLATE
COURTS, THE PARTIES HEREBY

                                      -9-
<PAGE>

IRREVOCABLY CONSENT TO THE JURISDICTION OF SUCH COURTS AND AGREE TO SAID VENUE.

     SECTION 16. WAIVER OF TRIAL BY JURY. TO THE EXTENT IT MAY LEGALLY DO SO,
THE COMPANY EXPRESSLY WAIVES ANY RIGHT TO TRIAL BY JURY OF ANY CLAIM, DEMAND,
ACTION, CAUSE OF ACTION OR PROCEEDING ARISING UNDER OR WITH RESPECT TO THIS
WARRANT CERTIFICATE OR IN ANY WAY CONNECTED WITH, OR RELATED TO, OR INCIDENTAL
TO, THE DEALINGS OF THE COMPANY AND THE HOLDER WITH RESPECT TO THIS WARRANT
CERTIFICATE OR THE TRANSACTIONS RELATED HERETO, IN EACH CASE WHETHER NOW
EXISTING OR HEREAFTER ARISING, AND IRRESPECTIVE OF WHETHER SOUNDING IN CONTRACT,
TORT OR OTHERWISE, TO THE EXTENT IT MAY LEGALLY DO SO, THE COMPANY AGREES THAT
ANY SUCH CLAIM, DEMAND, ACTION, CAUSE OF ACTION OR PROCEEDING SHALL BE DECIDED
BY A COURT TRIAL WITHOUT A JURY AND THAT THE HOLDER MAY FILE AN ORIGINAL
COUNTERPART OR A COPY OF THIS SECTION 16 WITH ANY COURT AS WRITTEN EVIDENCE OF
THE CONSENT OF THE COMPANY TO WAIVER OF ITS RIGHT TO TRIAL BY JURY.

     SECTION 17. Amendments; Modifications. This Warrant Certificate may be
amended or modified only with the written consent of the Company and the holders
representing a majority-in-interest of the then outstanding Investor Warrants
which holders shall include Generation Capital Associates, and any provision of
this Warrant Certificate may be waived only the party (or in the case of the
Holder, by holders representing a majority-in-interest of the then-outstanding
Investor Warrants which holders shall include Generation Capital Associates)
against whom enforcement of any waiver is sought; provided, that no such
amendment, modification or waiver shall be binding on a Holder without such
Holder's consent in the event that the amendment, modification or waiver (i)
increases the Exercise Price of any Investor Warrant; or (ii) reduces the amount
of Shares covered by any Investor Warrant.

     SECTION 18. Severability. The holding of any provision of this Warrant to
be invalid or unenforceable by a court of competent jurisdiction shall not
affect any other provision of this Warrant, which shall remain in full force and
effect. If any provision of this Warrant shall be declared by a court of
competent jurisdiction to be invalid, illegal or incapable of being enforced in
whole or in part, such provision shall be interpreted so as to remain
enforceable to the maximum extent permissible consistent with applicable law and
the remaining conditions and provisions or portions thereof shall nevertheless
remain in full force and effect and enforceable to the extent they are valid,
legal and enforceable, and no provisions shall be deemed dependent upon any
other covenant or provision unless so expressed herein.

     SECTION 19. Specific Performance. The Company acknowledges that irreparable
damage would occur to the Holder in the event that any of the provisions of this
Warrant Certificate were not performed by the Company in accordance with their
specific terms or were otherwise breached by the Company and that money damages
would not provide :an adequate remedy to the Holder. It is accordingly agreed
that the Holder shall be entitled to an injunction and other equitable remedies
to prevent breaches by the Company of this Warrant Certificate and to enforce
specifically the terms and provisions hereof in any court of the United States
or any state thereof or any other court having jurisdiction, this being in
addition to any other remedy to which the Holder may be entitled at law or in
equity or otherwise.

     SECTION 20. Captions. The section headings used herein are for convenience
only and shall not affect the construction hereof.

                                      -10-
<PAGE>

     IN WITNESS WHEREOF, the Company has caused this Warrant Certificate to be
duly executed under its corporate seal as of the Issue Date specified on the
face hereof.

                                 GENTIUM S.P.A.

                                 By:  __________________________
                                      Name:
                                      Title:

                  The issuer hereby expressly agrees that the competent
jurisdiction for any proceedings concerning this agreement is exclusively either
the Supreme Court of the State of New York in and for the County of New York or
the federal courts for such State and County, and all related appellate courts.

                                 GENTIUM S.P.A.

                                 By:  __________________________
                                      Name:
                                      Title:

                                      -11-
<PAGE>

                                    EXHIBIT A

<PAGE>

                                    EXHIBIT B

                          FORM OF ELECTION TO PURCHASE

     The undersigned hereby irrevocably elects to exercise the right,
represented by this Warrant Certificate, to purchase _______ shares of Common
Stock, par value (euro)1 per share, of Gentium S.p.A. (the "Company") and
herewith tenders payment of the exercise price, together with all applicable
transfer taxes, if any.

     Payment shall take the form of (check applicable box):

     [ ] wire transfer pursuant to the provisions of Section 1(b) of the Warrant
Certificate in the amount of $_____________, all in accordance with the terms
thereof; or

     [ ] the cancellation of such number of Shares as is necessary, in
accordance with the formula set forth in Section 1(f), to exercise this Warrant
with respect to the maximum number of Shares purchasable pursuant to the
cashless exercise procedure set forth in Section 1(f).

     The undersigned requests that a certificate for such shares of Common Stock
be registered in the name of ________________ whose address is
__________________ and that such certificate be delivered to
__________________________ whose address is ____________________.

Dated:                                Signature_______________

                                        (Signature must conform in all
                                        respects to name of holder as
                                        specified on the face of the
                                        Warrant Certificate.)

                                  ____________
                        (Insert Social Security or Other
                          Identifying Number of Holder)

<PAGE>

                                    EXHIBIT C

                                  TRANSFER FORM

     For value received, the undersigned Holder of the within Warrant
Certificate hereby sells, assigns and transfers unto the transferee whose name
and address are set forth below all of the right, title and interest of the
undersigned in, to and under the within Warrants (to the extent of the portion
of the within Warrant Certificate being transferred hereby, which portion is
_________ Warrants).

         Name of Transferee:___________________________________________________
         State of Organization (if applicable):________________________________
         Federal Tax Identification or Social Security Number:_________________
         Address:______________________________________________________________

     If such portion of the Warrants being transferred shall not consist of all
of the within Warrant Certificate, then the undersigned hereby requests that, as
provided in Section 5 of the within Warrant Certificate, a new Warrant
Certificate of like tenor respecting the balance of the Warrants not being
transferred pursuant hereto be issued in the name of and delivered to the
undersigned.

Dated:  ______________
                                                               [HOLDER]

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

                                       (Signature must conform in all
                                       respects to name of holder as
                                       specified on the face of the
                                       Warrant Certificate.)

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