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                                                                     Exhibit 2.2


                              AMENDED AND RESTATED
                               GUARANTY AGREEMENT

     THIS AMENDED AND RESTATED GUARANTY AGREEMENT, effective as of February 28,
2002 (the "Amended and Restated Guaranty Agreement"), is given by

     QIAGEN Sciences, Inc, a Maryland Corporation ("Guarantor"); and extended to

     QIAGEN GmbH, a German limited liability company (the "Lender"), party to
that certain amended and restated promissory note of even date herewith in the
original principal amount of Forty Three Million Four Hundred Seventy Five
Thousand and No/100 Dollars ($43,475,000.00) (such amended and restated
promissory note, as the same may be further modified or amended from time to
time, being hereinafter referred to as the "Note") from QIAGEN North American
Holdings, Inc., a California corporation (the "Borrower") to the Lender.

     This Amended and Restated Guaranty Agreement is made by Guarantor, and
accepted by Lender, in full substitution of the Guaranty Agreement, dated
November 5, 2001, made by Guarantor and extended to Lender, guaranteeing the
Borrower's obligation under the Note to repay the principal amount of Fifty
Million Euros (EUR 50.000.000) (the "Original Guaranty"). This Amended and
Restated Guaranty constitutes a modification of the amount and currency of
Guarantor's obligations under the Original Guaranty, and does not cancel such
obligations.

     NOW, THEREFORE, in consideration of the obligation of the Lender to make
the loan contemplated by the Note, and for other good and valuable
consideration, receipt whereof is hereby acknowledged, Guarantor hereby agrees
as follows:

     1. Guaranty Agreement of Payment. Guarantor hereby unconditionally
guarantees to the Lender by way of an independent guaranty the payment up to an
amount of Forty Three Million Four Hundred Seventy Five Thousand and No/100
Dollars ($43,475,000.00) when due, by acceleration or otherwise, of the
Obligations. For the purposes hereof, the term "Obligations" means any and all
obligations and liabilities under the Note, now existing or hereafter arising,
due or to become due, direct or indirect, absolute or contingent, howsoever
evidenced, held or acquired, as such Obligations may be modified, extended,
renewed or replaced from time to time. The guaranty of Guarantor as set forth in
this section is a guaranty of payment and not of collection.

        Guarantor shall effect payment hereunder to the Lender within fifteen
(15) days upon the Lender's demand and confirmation that the amount claimed from
Guarantor is equal to the monies which the Borrower has not paid when due.

     2. Release of Collateral, Parties Liable, etc. Guarantor agrees that the
whole or any part of any security now or hereafter held for the Obligations may
be exchanged, compromised, released or surrendered from time to time; that the
Lender shall not have any obligation to protect, perfect, secure or insure any
liens now or hereafter held for the Obligations or the properties subject
thereto; that the time or place of payment of the Obligations may be changed or
extended,

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in whole or in part, to a time certain or otherwise, and may be renewed or
accelerated, in whole or in part; that the Borrower may be granted indulgences
generally; that any provisions of the Note or any other documents executed in
connection with this transaction may be modified, amended or waived; that any
party liable for the payment of the Obligations may be granted indulgences or
released; and that any deposit balance for the credit of the Borrower or any
other party liable for the payment of the Obligations or liable upon any
security therefor may be released, in whole or in part, at, before and/or after
the stated, extended or accelerated maturity of the Obligations, all without
notice to or further assent by Guarantor, who shall remain bound thereon,
notwithstanding any such exchange, compromise, surrender, extension, renewal,
acceleration, modification, indulgence or release.

     3. Waiver of Rights. Guarantor expressly waives: (a) notice of acceptance
of this Amended and Restated Guaranty Agreement by the Lender and of all
extensions of credit to the Borrower by the Lender; (b) presentment of any of
the Obligations; (c) protest and notice of dishonor or of default to Guarantor
or to any other party with respect to the Obligations or with respect to any
security therefor; and (d) notice of the Lender obtaining, amending,
substituting for, releasing, waiving or modifying any security interest, liens,
or the encumbrances now or hereafter securing the Obligations, or a Lender's
subordinating, compromising, discharging or releasing such security interests,
liens or encumbrances; (e) all other notices to which Guarantor might otherwise
be entitled; and (f) any right to assert against the Lender, as a defense,
counterclaim, set-off or cross-claim, any defense (legal or equitable), set-off,
counterclaim or claim which Guarantor may now or hereafter have against the
Lender or the Borrower, but such waiver shall not prevent Guarantor from
asserting against the Lender in a separate action, any claim, action, cause of
action, or demand that Guarantor might have, whether or not arising out of this
Amended and Restated Guaranty Agreement.

     4. Primary Liability of Guarantor. Guarantor agrees that this Amended and
Restated Guaranty Agreement may be enforced by the Lender without the necessity
at any time of resorting to or exhausting any other security or collateral and
without the necessity at any time of having recourse to the Borrower under the
Note or any collateral now or hereafter securing the Obligations or otherwise,
and Guarantor hereby waives the right to require the Lender to proceed against
the Borrower or any other person (including a co-guarantor) or to require the
Lender to pursue any other remedy or enforce any other right. Guarantor further
agrees that it shall have no right of subrogation, reimbursement or indemnity
whatsoever, nor any right of recourse to security, if any, for the Obligations,
so long as any amounts payable to the Lender in respect of the Obligations shall
remain outstanding and until all of the commitments of Lender, if any, under the
Note shall have expired or been terminated. Guarantor further agrees that
nothing contained herein shall prevent the Lender from suing the Borrower with
respect to its obligations under the Note or foreclosing its security interest
in or lien on any collateral now or hereafter securing the Obligations or from
exercising any other rights available to the Lender under the Note if neither
the Borrower nor Guarantor timely performs the obligations of the Borrower
thereunder, and the exercise of any of the aforesaid rights and the completion
of any foreclosure proceedings shall not constitute a discharge of Guarantor's
obligations hereunder unless as a result thereof the Obligations shall have been
paid in full and any all commitments have expired or been terminated; it being
the purpose and intent of Guarantor that Guarantor's obligations hereunder shall
be absolute, irrevocable, independent and unconditional under any and all
circumstances. Neither Guarantor's obligations under this Amended and Restated
Guaranty Agreement nor any

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remedy for the enforcement thereof shall be impaired, modified, changed or
released in any manner whatsoever by an impairment, modification, change,
release or limitation of the liability of the Borrower, by reason of the
Borrower's bankruptcy or insolvency or by reason of the invalidity or
unenforceability of all or any portion of the Obligations. Guarantor
acknowledges that the term "Obligations" as used herein includes any payments
made by the Borrower to the Lender and subsequently recovered by the Borrower or
a trustee for the Borrower pursuant to the Borrower's bankruptcy or insolvency
and that the guaranty of Guarantor hereunder shall be reinstated to the extent
of such recovery.

     5. Attorneys' Fees and Costs of Collection. If at any time or times
hereafter the Lender employs counsel to pursue collection, to intervene, to sue
for enforcement of the terms hereof or of the Note or any other of the credit
documents, or to file a petition, complaint, answer, motion or other pleading in
any suit or proceeding relating to this Amended and Restated Guaranty Agreement,
the Note or any other of the credit documents related to the Note, then in such
event, all of the actual and reasonable attorneys' fees relating thereto shall
be an additional liability of Guarantor to the Lenders hereunder, payable on
demand.

     6. Right of Set-Off. After the occurrence of any default or event of
default under the Note, the Lender may set-off any matured obligation owed by
Guarantor under this Amended and Restated Guaranty Agreement (to the extent
beneficially owned or held by the Lender) against any obligation (whether or not
matured) owed by the Lender to Guarantor, regardless of the place of payment,
booking branch or currency of either obligation. If the obligations are in
different currencies, the Lender may convert either obligation at a market rate
of exchange in its usual course of business for the purpose of the set-off. If
either obligation is unliquidated or unascertained, the Lender may set-off in
any amount estimated by it in good faith to be the amount of that obligation.

     7. Term of Guarantee. This Amended and Restated Guaranty Agreement shall
continue in full force and effect until the Obligations are fully and
indefeasibly paid, performed and discharged, and all commitments of the Borrower
under the Note have expired or been terminated. This Amended and Restated
Guaranty Agreement covers the Obligations whether presently outstanding or
arising subsequent to the date hereof including all amounts advanced by any
Lender in stages or installments. Notwithstanding the foregoing, this Amended
and Restated Guaranty Agreement shall continue to be effective, or be
reinstated, as the case may be, if at any time payment, or any part thereof, of
any of the Obligations is rescinded or must otherwise be restored or returned by
a Lender upon the insolvency, bankruptcy, dissolution, liquidation or
reorganization of the Borrower, or upon or as a result of the appointment of a
receiver, intervenor or conservator of, or trustee or similar officer for, the
Borrower or any substantial part of its property, or otherwise, all as though
such payments had not been made. Guarantor warrants and represents to the Lender
that (i) Guarantor has the power and authority to enter into this Amended and
Restated Guaranty Agreement and to perform its obligations hereunder and has by
proper corporate action duly authorized the execution and delivery of this
Amended and Restated Guaranty Agreement, (ii) this Amended and Restated Guaranty
Agreement is binding upon and enforceable against Guarantor in accordance with
its terms and (iii) the execution and delivery of this Amended and Restated
Guaranty Agreement does not violate or constitute a breach of the charter
documents or by-laws of Guarantor or any agreement to which Guarantor is a party
or of any applicable laws.

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     8. Further Representations and Warranties. Guarantor agrees that the Lender
will not have any obligation to investigate the financial condition or affairs
of the Borrower for the benefit of Guarantor nor to advise Guarantor of any fact
respecting, or any change in, the financial condition or affairs of the Borrower
which might come to the knowledge of the Lender at any time, whether or not the
Lender knows or believes or has reason to know or believe that any such fact or
change is unknown to Guarantor or might (or does) materially increase the risk
of Guarantor as a guarantor or might (or would) affect the willingness of
Guarantor to continue as a guarantor with respect to the Obligations.

     9. Additional Liability of Guarantor. If Guarantor is or becomes liable for
any indebtedness owing by the Borrower to the Lender by endorsement or otherwise
other than under this Amended and Restated Guaranty Agreement, such liability
shall not be in any manner impaired or reduced hereby but shall have all and the
same force and effect it would have had if this Amended and Restated Guaranty
Agreement had not existed and Guarantor's liability hereunder shall not be in
any manner impaired or reduced thereby.

     10. Cumulative Rights. All rights of the Lender hereunder or otherwise
arising under any documents executed in connection with or as security for the
Obligations are separate and cumulative and may be pursued separately,
successively or concurrently, or not pursued, without affecting or limiting any
other right of the Lender and without affecting or impairing the liability of
Guarantor.

     11. Usury. Notwithstanding any other provisions herein contained, no
provision of this Amended and Restated Guaranty Agreement shall require or
permit the collection from Guarantor of interest in excess of the maximum rate
or amount that Guarantor may be required or permitted to pay pursuant to any
applicable law. In the event any such interest is collected, it shall be applied
in reduction of Guarantor's obligations hereunder, and the remainder of such
excess collected shall be returned to Guarantor once such obligations have been
fully satisfied.

     12. The Lender. Guarantor shall pay (i) all actual and reasonable
out-of-pocket expenses of the Lender in connection with the administration of
this Amended and Restated Guaranty Agreement and the transactions hereunder, any
waiver or consent hereunder or any amendment hereof or any default or alleged
default hereunder, or (ii) if default occurs, all out-of-pocket expenses
incurred by the Lender, including fees and disbursements of counsel, actually
incurred in connection with such default and collection, bankruptcy, insolvency
and other enforcement proceedings resulting therefrom. In addition, Guarantor
shall indemnify and defend the Lender and its respective directors, officers,
agents, employees and affiliates from, and hold each of them harmless against,
any and all losses, liabilities, claims, damages or expenses incurred by any of
them arising out of or by reason of any investigation, litigation or other
proceeding brought or threatened relating to this Amended and Restated Guaranty
Agreement, including, but without limitation, amounts paid in settlement, court
costs, and fees and disbursements of counsel incurred in connection with any
such investigation, litigation or other proceedings. The foregoing
indemnification shall survive the repayment of the Obligations and the
termination of this Amended and Restated Guaranty Agreement. Guarantor hereby
releases the Lender from any liability for any act or omission relating to this
Amended and Restated Guaranty Agreement, except such as may result from the
Lender's gross negligence or willful misconduct.

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     13. Successors and Assigns. This Amended and Restated Guaranty Agreement
shall be binding on and enforceable against Guarantor and its successors and
assigns; provided that, Guarantor may not assign or transfer any of its
obligations hereunder without prior written consent of the Lender. This Amended
and Restated Guaranty Agreement is intended for and shall inure to the benefit
of the Lenders and each and every person who shall from time to time be or
become the owner or holder of any of the Obligations, and each and every
reference herein to "Lender" shall include and refer to each and every successor
or assignee of a Lender at any time holding or owning any part of or interest in
any part of the Obligations. This Amended and Restated Guaranty Agreement shall
be transferable and negotiable with the same force and effect, and to the same
extent, that the Obligations are transferable and negotiable, it being
understood and stipulated that upon assignment or transfer by the Lender of any
of the Obligations the legal holder or owner of the Obligations (or a part
thereof or interest therein thus transferred or assigned by the Lender) shall
(except as otherwise stipulated by the Lender in its assignment) have and may
exercise all of the rights granted to the Lender under this Amended and Restated
Guaranty Agreement to the extent of that part of or interest in the Obligations
thus assigned or transferred to said person. Guarantor expressly waives notice
of transfer or assignment of the Obligations, or any part thereof, or of the
rights of the Lender hereunder. Failure to give notice will not affect the
liabilities of Guarantor hereunder.

     14. Application of Payments. The Lender may apply any payments received by
it from any source against that portion of the Obligations (principal, interest,
court costs, attorneys' fees or other) in such priority and fashion as it may
deem appropriate subject to the terms and provisions of the Note.

     15. Modifications. This Amended and Restated Guaranty Agreement and the
provisions hereof may be changed, discharged or terminated only by an instrument
in writing signed by Guarantor and the Lender

     16. Notices. All notices, requests and other communications to any party
hereunder shall be in writing and shall be given to such party: (a) at its
address or facsimile number set forth on the signature pages hereof, or (c) at
such other address or facsimile number as such party may hereafter specify for
the purpose by notice to the other party. Each such notice, request or other
communication shall be effective (i) if given by facsimile, when such facsimile
is transmitted to the facsimile number specified in this Section and the
appropriate confirmation slip is received, (ii) if given by mail, 72 hours after
such communication is deposited in the mails with first class postage prepaid,
addressed as aforesaid or (iii) if given by any other means, when delivered at
the address specified in this Section.

     17. Severability. In the event that any provision hereof shall be deemed to
be invalid by reason of the operation of any law or by reason of the
interpretation placed thereon by any court, this Amended and Restated Guaranty
Agreement shall be construed as not containing such provision, but only as to
such jurisdictions where such law or interpretation is operative, and the
invalidity of such provision shall not affect the validity of any remaining
provision hereof, and any and all other provisions hereof which are otherwise
lawful and valid shall remain in full force and effect.

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     18. Governing Law; Submission to Jurisdiction; Venue; Waiver of
Jury Trial; etc.
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         (a) THIS AMENDED AND RESTATED GUARANTY AGREEMENT SHALL BE GOVERNED BY
AND CONSTRUED AND INTERPRETED IN ACCORDANCE WITH THE LAWS OF THE STATE OF
MARYLAND. Guarantor hereby submits to the non-exclusive jurisdiction of the
United States District Court for Maryland or the courts of the State of Maryland
in Montgomery County for the purposes of any legal action or proceeding with
respect to this Amended and Restated Guaranty Agreement. Guarantor irrevocably
waives, to the fullest extent permitted by law, any objection which it may now
or hereafter have to the laying of the venue of any such proceeding brought in
such a court and any claim that such proceeding has been brought in an
inconvenient form. Guarantor hereby consents to process being served in any such
proceeding by the mailing of a copy thereof by registered or certified air mail,
postage prepaid, return receipt requested, to the address for notices to
Guarantor specified in Section 16 above or in any other matter permitted by law.
Nothing herein shall affect the right of the Lender to serve process in any
other manner permitted by law or to commence legal proceedings or to otherwise
proceed against Guarantor in any other jurisdiction.

         (b) GUARANTOR HEREBY IRREVOCABLY WAIVES ALL RIGHT TO TRIAL BY JURY IN
ANY ACTION, PROCEEDING OR COUNTERCLAIM ARISING OUT OF OR RELATING TO THIS
AMENDED AND RESTATED GUARANTY AGREEMENT.

         (c) All payments made by Guarantor hereunder shall be made free and
clear of, and without deduction or withholding for or on account of, any present
or future income, stamp or other taxes, levies, imposts, duties, charges, fees,
deductions, or withholdings, now or hereafter imposed, levied, collected,
withheld or assessed by any court, or governmental body, agency, or other
official, excluding (i) taxes measured by or imposed upon the overall net income
or receipts of Lender, and all franchise taxes, branch taxes, taxes on doing
business, or taxes on the overall capital or net worth of Lender, in each case
imposed in lieu of or in addition to net income taxes, or (ii) any taxes arising
after the date hereof solely as a result of or attributable to Lender changing
any applicable lending office after the date that such Lender becomes a party
hereto, imposed (A) by the jurisdiction under the laws of which a Lender,
applicable lending office, branch or affiliate is organized or is located, or in
which its principal executive office is located, or any nation within which such
jurisdiction is located, or any political subdivision thereof; or (B) by reason
of any connection between the jurisdiction imposing such tax and the Lender,
applicable lending office, branch or affiliate other than a connection arising
solely from a Lender having executed, delivered or performed its obligations, or
received payment under or enforced, this Amended and Restated Guaranty
Agreement. If any such non excluded taxes, levies, imposts, duties, charges,
fees, deductions or withholdings ("Non Excluded Taxes") are required to be
withheld from any amounts payable to Lender hereunder, (1) the amounts so
payable to Lender shall be increased to the extent necessary to yield to Lender
(after payment of all Non Excluded Taxes) interest or any such other amounts
payable hereunder at the rates or in the amounts specified in this Amended and
Restated Guaranty Agreement, provided however, that Guarantor shall be entitled
to deduct and withhold any Non Excluded taxes and shall not be required to
increase any such amounts payable to Lender that is not organized under the laws
of the United States of America or a state thereof if such Lender fails to, on
or before the date of any payment by Guarantor under this Amended and Restated
Guaranty Agreement to the Lender, deliver to Guarantor the appropriate forms
certifying that it is entitled to receive payments under

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this Amended and Restated Guaranty Agreement without deduction or withholding of
any United States federal income taxes and that it is entitled to an exemption
from United States backup withholding tax, whenever any Non Excluded Taxes are
payable by Guarantor, and (2) as promptly as reasonably practicable thereafter
Guarantor shall send to the Lender a certified copy of an original official
receipt received by Guarantor showing payment thereof. If Guarantor fails to pay
any Non Excluded Taxes when due to the appropriate taxing authority, or fails to
remit required receipts or other required documentary evidence, Guarantor shall
indemnify the Lender for any incremental taxes, interest or penalties that may
become payable by the Lender as a result of such failure.

     19. Headings. The headings in this instrument are for convenience of
reference only and shall not limit or otherwise affect the meaning of any
provisions hereof.

     20. Counterparts. This Amended and Restated Guaranty Agreement may be
executed in any number of counterparts and by different parties hereto on
separate counterparts, each constituting an original, but all together one and
the same instrument.

     IN WITNESS WHEREOF, Guarantor has caused this Amended and Restated Guaranty
Agreement to be duly executed under seal by its duly authorized officers as of
the date first above written.

Date: February 28, 2002                              QIAGEN Sciences, Inc.
                                                     19825 Executive Park Circle
                                                     Germantown, Maryland 20874

                                                     By: /s/ Michael Burgett
                                                        --------------------
                                                        Michael Burgett
                                                        Vice President



                              ACCEPTANCE BY LENDER:

     The foregoing Amended and Restated Guaranty Agreement is hereby accepted by
Lender in full substitution for the Original Guaranty (as defined herein). The
Original Guaranty is hereby canceled.

Executed as of February 28, 2002

QIAGEN GmbH

By: /s/ Peer Schatz
   -----------------------
   Peer Schatz
   Chief Financial Officer