Document:

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                                                                  EXHIBIT 10.18

                       GUARANTY AND SURETYSHIP AGREEMENT

         This Guaranty and Suretyship Agreement is executed as of this 21st day
of June, 2002, by SYMBION, INC., a Tennessee corporation (the "Guarantor") in
favor of U.S. Bank National Association and its successors and assigns
("Bank").

                                    RECITALS

         At the request of Guarantor, Bank has acquired indebtedness of
Wilmington Surgery Center, L.P., a Tennessee limited partnership (the
"Borrower") to Bank of America, N.A. ("Bank of America") Execution of this
Guaranty and Suretyship Agreement is a condition to such acquisition by Bank.

         FOR VALUE RECEIVED and intending to be legally bound, in consideration
of credit given, or to be given, advances made or to be made, or other
financial accommodations from time to time afforded or to be afforded to
Borrower, the Guarantor hereby, unconditionally and irrevocably guarantees and
becomes surety to Bank for the due and punctual payment and performance of the
Obligations (as hereinafter defined), as and when such payment or performance
shall respectively become due, payable, and/or performed in accordance with the
terms of the Obligations, whether at maturity or by declaration, acceleration,
or otherwise. Capitalized terms not otherwise defined herein shall have the
meanings ascribed to such terms in the Loan Agreement (as hereinafter defined).

                               I.   DEFINITIONS

         As used herein, the following terms shall have the indicated meanings:

         "Agreement" means this Guaranty and Suretyship Agreement and all
modifications, renewals, extensions, and amendments hereto.

         "Collateral" means the collateral securing, or which may in the future
secure the Obligations.

         "Loan Agreement" means that certain Loan Agreement dated May 24, 1999
among the Borrower, Bank of America and Symbion Ambulatory Resource Centres,
Inc., together with any amendments, renewals, extensions, or restatements
thereof, such agreement having been assigned to Bank.

         "Note" means the Promissory Note dated May 24, 1999, in the original
principal amount of $8,000,000.00, made by Borrower and payable to Bank of
America, together with all amendments, renewals and extensions thereof, such
agreement having been assigned to Bank.

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         "Obligations" means and includes (i) all indebtedness of Borrower to
Bank evidenced by the Note, and all other indebtedness of Borrower to Bank,
whether such indebtedness is direct or indirect, absolute or contingent, joint
or several, together with any and all indebtedness created or incurred under
any extension, renewal, refinancing, or refunding of such indebtedness in whole
or in part, whether on account of principal, interest, or otherwise (including,
without limitation, any interest which accrues after the commencement of any
case, proceeding, or other action relating to the bankruptcy, insolvency, or
reorganization of a Borrower), (ii) payment, performance, and discharge of all
other obligations of Borrower under the Loan Documents, (iii) all costs and
expenses, including without limitation reasonable attorneys' fees, incurred by
Bank in the collection or attempted collection of any indebtedness included in
the Obligations, and in the administration of the Obligations, and (iv) all
future advances made by Bank for the maintenance, preservation, protection, or
enforcement of, or realization upon, the property subjected and intended to be
subjected to the lien and security interest in the Collateral, or any portion
thereof, including without limitation advances for storage, transportation
charges, taxes, insurance, repairs, and the like.

                                II.   COVENANTS

         1.       The obligations of Guarantor under this Agreement shall be
continuing, absolute, and unconditional and shall remain in full force and
effect without regard to, and shall not be released, discharged, or in any way
affected by: (1) any amendment, extension, modification of, or supplement to
the Loan Documents, including without limitation an increase in the principal
indebtedness evidenced by the Note; (2) any exercise or nonexercise of or delay
in exercising any right, remedy, power, or privilege under or in respect of
this Agreement, the Loan Agreement, or any of the other Loan Documents (even if
any such right, remedy, power, or privilege shall be lost thereby), or any
waiver, consent, indulgence, or other action or inaction in respect thereof;
(3) any lack of diligence, failure, neglect, or omission on the part of Bank to
make any demand or protest or to give any notice of dishonor or default; (4)
any failure or omission of Bank to realize upon or protect any of the
Collateral, to exercise or enforce any lien upon the Collateral, or to exercise
any right of set-off; (5) any bankruptcy, insolvency, arrangement, composition,
assignment for the benefit of creditors, or similar proceeding commenced by or
against Borrower or Guarantor; (6) any failure to perfect or continue
perfection of, or any release or waiver of, any rights given to Bank with
respect to any property as security for the performance of any of Borrower's or
Guarantor's obligations under the Loan Agreement, the Note, or any other Loan
Document; (7) any extension of time for payment or performance of any of the
Obligations; (8) dissolution (voluntarily or involuntarily) of Guarantor; (9)
the genuineness, validity, or enforceability of the Loan Documents; (10) any
limitation of liability of Borrower or Guarantor contained in the Loan
Documents; (11) any defense that may arise by reason of the failure of Bank to
file or enforce a claim

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against Borrower or Guarantor in any bankruptcy or other proceeding; (12) the
voluntary or involuntary liquidation, dissolution, sale of all or substantially
all of the property of Borrower or Guarantor, the marshalling of assets and
liabilities, or other similar proceeding affecting Borrower or any of their
respective assets; (13) the release of Borrower or Guarantor from the
performance or observance of any of the agreements, covenants, terms, or
conditions contained in the Loan Documents by operation of law; (14) the
release or discharge of any other surety or guarantor of the Obligations; or
(15) any other circumstances which might otherwise constitute a legal or
equitable discharge of, or defense available to, a guarantor or surety.

         2.       Guarantor agrees that so long as this Agreement is in effect
Guarantor will maintain Guarantor's corporate existence and will not dissolve
or otherwise dispose of all or substantially all of Guarantor's assets.

                                III.   WAIVERS

         1.       Guarantor hereby waives and agrees not to exercise any rights
which it may acquire by way of subrogation or reimbursement under this Guaranty
as a result of any payment made hereunder or otherwise.

         2.       Guarantor hereby waives (a) any presentment for payment,
notice of nonpayment, demand, protest, or notice of acceptance of this
Agreement, (b) any right to notice of advances made to Borrower from time to
time under the provisions of the Loan Documents, and (c) any notice of any
matters described or referred to in Article II above; provided, however, that
Guarantor does not waive any rights prior to default that, pursuant to Section
9-602 of the Revised Article 9, may not be waived.

         3.       Guarantor hereby further waives any and all notice of every
kind to which Guarantor might otherwise be entitled with respect to the
incurring of any further or increased obligation or liability by Borrower to
Bank, the demand for payment or the payment of all or any obligations or
liabilities of Borrower or Guarantor to Bank (whether now existing or hereafter
arising) or the presentment of any instrument for payment at any time in
connection with any obligation or liability of Borrower or Guarantor or the
protest or nonpayment thereof. Guarantor hereby further waives, surrenders, and
agrees not to claim or enforce (i) any right to be subrogated in whole or in
part of any right or claim of Bank against Borrower or Guarantor arising under
the Loan Documents or any other collateral given to Bank as security for the
payment or performance of the Obligations and (ii) any right to require the
marshalling of any assets of Borrower or Guarantor, which right of subrogation
or marshalling might otherwise arise from any partial payment of the
Obligations by Guarantor. Guarantor hereby further waives all applicable
statutes of limitation which may exist at any time in favor of Guarantor.

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                     IV.   REPRESENTATIONS AND WARRANTIES

         Guarantor represents, warrants, and covenants to and with Bank that:

         1.       Guarantor acknowledges that this Agreement is necessary to
induce Bank to advance the credit for the Obligations and Guarantor is willing
and able to deliver this Agreement because Guarantor will receive direct and
material benefit from Bank's extension of credit to Borrower.

         2.       Guarantor is now and will be completely familiar with the
business, operations, and condition of Borrower and Guarantor hereby waives and
relinquishes any duty on the part of Bank to disclose any matter, fact, or
thing relating to the business, operation, or condition of Borrower now known
or hereafter known by Bank.

                         V.   DEFAULT AND ENFORCEMENT

         1.       In addition to all liens upon and rights of set-off against
moneys, securities, or other property of Guarantor given to Bank by law or
equity, Bank shall have a lien upon, security interest in, and right of
immediate set-off against all moneys, instruments, notes, bonds, commercial
paper, securities, and other property of Guarantor now or hereafter in the
possession of or on deposit with Bank, whether held in a general or special
account for deposit, safe-keeping, or otherwise. Every such lien and right of
set-off may be exercised after the occurrence of an Event of Default under the
Loan Agreement (and expiration of all notice and cure periods), or a default by
Guarantor under this Agreement, and expiration of applicable cure periods,
without further notice or demand to Guarantor, and Bank may sell or cause to be
sold, at public or private sale, in any manner and place which may be lawful,
for cash or credit and upon such terms as Bank may see fit, and without demand
or notice to Guarantor, all or any of such property, and Bank or any other
person may purchase such property, rights, or interests so sold and thereafter
hold the same free of any claim or right of whatsoever kind, including any
right of equity or redemption of Guarantor, such demand, notice, or right of
equity or redemption being hereby expressly waived and released.

         2.       Each and every right, remedy, and power hereby granted to
Bank or allowed it by law or other agreement shall be cumulative and not
exclusive of any other, and may be exercised by Bank at any time and from time
to time. In the event that the Obligations of Borrower to Bank exceed in any
respect any amount by which this Agreement may be limited, any payments by
Borrower, or any collections or recovery by Bank from any sources other than
this Agreement, may be applied first by Bank to any portion of the Obligations
which exceeds the limits of this Agreement.

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         3.       Notwithstanding anything contained in this Agreement or in
the Loan Documents to the contrary, Guarantor shall be in default under this
Agreement upon the occurrence of an Event of Default under the Loan Agreement
(and expiration of applicable cure periods). Upon the occurrence of any such
default, Bank may, at its option, accelerate the indebtedness evidenced and
secured by the Loan Documents.

         4.       This shall be an agreement of suretyship as well as of
guaranty, and Bank may proceed directly against Guarantor whenever any payment
or performance required pursuant to the Obligations is not made or rendered to
Bank without being required to make demand upon or proceed first against
Borrower or any other person or entity, or against any security for Borrower's
or Guarantor's Obligations under the Loan Documents or hereunder, or exhaust
its remedies against Borrower or any other surety or guarantor. It is expressly
agreed that Bank may at any time following an Event of Default under the Loan
Agreement or a default by Guarantor hereunder, make demand for payment on, or
bring a claim against, Guarantor.

         5.       If Bank employs counsel to enforce this Agreement by suit or
otherwise, Guarantor will reimburse Bank, upon demand, for all expenses
incurred in connection therewith (including, without limitation, reasonable
attorneys' fees), whether or not suit is actually instituted.

         6.       Guarantor irrevocably: (a) agrees that Bank or any other
holder or holders of the Note may bring suit, action, or other legal
proceedings arising out of this Guaranty or the transactions contemplated
hereby in the courts of the State of Tennessee, sitting in Nashville, Davidson
County, Tennessee, or the courts of the United States for the Middle District
of Tennessee, sitting in Nashville, Davidson County, Tennessee, but shall not
be restricted to such courts; (b) consents to the jurisdiction of each such
court in any such suit, action, or proceeding; and (c) waives any objection
which Guarantor may have to the laying of the venue of any such suit, action,
or proceeding in any of such courts.

                           VI.   GUARANTY LIABILITY

         1.       Guarantor's obligations hereunder and under the other Loan
Documents shall be in an amount (such amount being referred to herein as the
"Maximum Guaranty Liability") equal to, but not in excess of, the maximum
liability permitted under Title 11 of the United States Code, any other state
or federal laws governing bankruptcy, suspension of payments, reorganization,
arrangement, adjustment of debts, dissolution, insolvency, relief of debtors or
creditors' rights and any other similar laws ("Applicable Bankruptcy Law"). To
the extent such obligations otherwise would be subject to avoidance under
Applicable Bankruptcy Law, if Guarantor is deemed not to have received valuable

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consideration, fair value or reasonably equivalent value for its obligations
hereunder or under the other Loan Documents, Guarantor's obligations hereunder
and under the other Loan Documents shall be reduced to that amount which, after
giving effect thereto, would not render Guarantor insolvent, or leave Guarantor
with an unreasonably small capital to conduct its business, or cause Guarantor
to have incurred debts (or to be deemed to have intended to incur debts),
beyond its ability to pay such debts as they mature, at the time such
obligations are deemed to have been incurred under Applicable Bankruptcy Law.
As used herein, the terms "insolvent" and "unreasonably small capital" shall
likewise be determined in accordance with Applicable Bankruptcy Law. This
Paragraph 1 is intended solely to preserve the rights of the Bank hereunder and
under the other Loan Documents to the maximum extent permitted by Applicable
Bankruptcy Law, and neither the Guarantor nor any other person or entity shall
have any right or claim under this Paragraph 1 that otherwise would not be
available under Applicable Bankruptcy Law. Guarantor agrees that the
Obligations at any time and from time to time may exceed the Maximum Guaranty
Liability of Guarantor, without impairing this Guaranty or affecting the rights
and remedies of the Bank hereunder.

                             VII.   MISCELLANEOUS

         1.       In the event Bank is required at any time to refund or repay
to any person for any reason any sums collected by it on account of the
obligations subject to this Agreement, including but not limited to sums repaid
to a Trustee in Bankruptcy as a result of an avoided preferential transfer or
fraudulent conveyance, Guarantor agrees that all such sums shall be subject to
the terms of this Agreement and that Bank shall be entitled to recover such
sums from Guarantor notwithstanding the fact that this Agreement previously may
have been returned to Guarantor or that Guarantor previously may have been
discharged from further liability under this Agreement.

         2.       Any notice, demand, or request by Bank to Guarantor or by
Guarantor to Bank shall be in writing and shall be given in accordance with the
Loan Agreement.

         3.       This Agreement constitutes the entire agreement, and
supersedes all prior agreements and understandings, both written and oral,
between Guarantor and Bank with respect to the subject matter hereof. If any
clause, provision, or section of this Agreement is determined to be illegal or
invalid by any court, the invalidity of such clause, provision, or section
shall not affect any of the remaining clauses, provisions, or sections hereof
and this Agreement shall be construed and enforced as if such illegal or
invalid clause, provision, or section had not been contained herein. In case
any agreement or obligation contained in this Agreement be held to be in
violation of law, then such agreement or obligation shall be deemed

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to be the agreement or obligation of Guarantor, as the case may be, to the full
extent permitted by law.

         4.       No set-off, claim, reduction, or diminution of any obligation
or defense of any kind or nature, which Guarantor or Borrower has or may have
against Bank, shall be available hereunder to Guarantor against Bank.

         5.       No act of commission or omission of any kind or at any time
on the part of Bank in respect of any matter whatsoever shall in any way effect
or impair this Agreement. This Agreement is in addition to and no in
substitution for or discharge of any other suretyship held by Bank.

         6.       This Agreement shall be construed and enforced in accordance
with, and the rights of the parties shall be governed by, the laws of the State
of Tennessee. The invalidity or unenforceability of any one or more phrases,
sentences, clauses, or provisions in this Agreement shall not affect the
validity or enforceability of the remaining portions of this Agreement or any
part thereof.

         7.       This Agreement shall bind Guarantor and Guarantor's
successors and assigns and the benefits hereof shall inure to its successors
and assigns. Bank may, without any notice whatsoever to Guarantor, sell,
assign, or transfer all or any part of the Obligations, and in that event each
and every immediate and successive assignee, transferee, or holder of all or
any part of the Obligations shall have the right to enforce this Agreement, by
suit or otherwise, for the benefit of such assignee, transferee, or holder, as
fully as though such assignee, transferee, or holder were herein by name given
such rights, powers, and benefits; provided, however, that Bank shall have an
unimpaired right, prior and superior to that of any assignee, transferee, or
holder, to enforce this Agreement for the benefit of Bank as to so much of the
Obligation that Bank has not sold, assigned, or transferred.

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         WITNESS the due execution hereof as of the date first written above.

SYMBION, INC.

BY:
   -------------------------------------

TITLE:
      ----------------------------------------<PAGE>
                                                                  EXHIBIT 10.27

                 THIRD AMENDMENT TO LOAN AND SECURITY AGREEMENT

         THIS THIRD AMENDMENT (this "Amendment"), made this ____ day of June,
2002, is by and among U.S. Bank National Association (the "Bank") the successor
to Bank of America, N.A., the successor to NationsBank, N.A. ("Bank of
America"), ARC of Bellingham, L.P., a Tennessee limited partnership (the
"Borrower") and Symbion Ambulatory Resource Centres, Inc., a Tennessee
corporation and the successor to Ambulatory Resource Centres, Inc. (the
"Guarantor").

                                    RECITALS

         Bank of America has previously made a loan to the Borrower, an
Affiliate of Guarantor, pursuant to a Loan and Security Agreement dated
September 7, 1999 (as amended from time to time, the "Loan Agreement").
Capitalized terms not otherwise defined in this Amendment shall have the
meaning provided in the Loan Agreement. The Loan Agreement has been amended
pursuant to (i) a First Amendment to Loan and Security Agreement dated April
12, 2000 among Bank of America, Borrower and Guarantor, and (ii) a Second
Amendment to Loan and Security Agreement dated March 29, 2001 among Bank of
America, Borrower and Guarantor. At the request of Borrower, Bank has acquired
all of Bank of America's interest in the indebtedness extended pursuant to the
Loan Agreement, conditioned upon the execution of this Amendment and compliance
with the terms hereof.

         NOW, THEREFORE, the parties to this Amendment hereby agree as follows:

Article I.        Amendment to Loan Agreement. The parties hereto amend the Loan
Agreement as follows:

         Section 1.1 The definition of "LOAN TERMINATION DATE" in the Loan
Agreement is hereby deleted in its entirety and replaced with the following:

                  `"LOAN TERMINATION DATE" means the earlier of (i) April 2,
         2003 or (ii) the financial closing of the credit facility
         substantially as described in the term sheet posted by Banc of America
         Securities LLC as of May 16, 2002 on IntraLinks.com.'

         Section 1.2 The following definitions are hereby added to the Loan
Agreement:

                  `"EBITDAR" means, for any Person and for any period of
         determination, the Net Income for such period plus (A) Interest

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         Expense for such period deducted in the determination of Net Income,
         (B) federal and state taxes for such period deducted in the
         determination of Net Income, (C) depreciation deducted in the
         determination of Net Income, (D) amortization deducted in the
         determination of Net Income, (E) non-cash or non-recurring charges for
         such period deducted in the determination of Net Income, and (F)
         Rental Expense for such period deducted in the determination of Net
         Income, all as determined in accordance with generally accepted
         accounting principles consistently applied.

                  "FIXED CHARGE COVERAGE RATIO" means the ratio of (A) the sum
         of EBITDAR, minus maintenance Capital Expenditures, minus cash
         payments of federal and state taxes to (B) the sum of Interest
         Expense, plus Rental Expense, plus scheduled principal payments on
         Indebtedness, measured on a trailing four quarters basis.

                  "TWELVE MONTH PRO-FORMA EFFECT" means, in making any
         calculation to determine if Symbion is in compliance with Subparagraph
         6.15(g) of the Loan Agreement, that the calculation will be made
         assuming that (a) any Acquisition made during the twelve-month period
         ending on the date of determination (the "Reference Period"), and (b)
         any Indebtedness associated with (a) incurred during the Reference
         Period or to be incurred as of the date of determination, were made or
         incurred on the first day of the Reference Period. Any funds to be
         used in consummating an Acquisition will be assumed to have been used
         for that purpose as of the first day of the Reference Period. If
         EBITDA for the Reference Period associated with the assets acquired or
         to be acquired in any Permitted Acquisition is greater than $0, such
         EBITDA will be included in the calculation of EBITDA, and any
         Indebtedness to be incurred in connection with the consummation of any
         Acquisition will be assumed to have been incurred on the first day of
         the Reference Period. Interest Expense with respect to such
         Indebtedness assumed to have been incurred on the first day of the
         Reference Period which bears interest at a floating rate shall be
         calculated at the current rate under the agreement governing such
         Indebtedness. Any Interest Expense incurred during the Reference
         Period which was or is to be refinanced with the proceeds of
         Indebtedness assumed to have been incurred as of the first day of the
         Reference Period will be excluded from the calculation for which a
         Pro-Forma Effect is being given.'

         Section 1.3 Section 2.2(a) of the Loan Agreement is hereby deleted in
its entirety and replaced with the following:

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                  "(a) Interest shall be charged and paid on the Loan from the
         date of the initial advance until the Loan is paid at a rate equal to
         the LIBO Rate plus three hundred fifty basis points (3.5%), to be
         adjusted at the beginning of each Interest Period."

         Section 1.4 The following is hereby added to the Loan Agreement as
Section 6.15(g):

                  "(g) At the end of each Quarterly Period, the Fixed Charge
         Coverage Ratio of Symbion, calculated on a consolidated basis and
         giving Twelve-Month Pro-Forma Effect to any Acquisition made and any
         Funded Debt incurred in connection therewith, shall be greater than
         1.25 to 1.00."

         Article II. General.

         Section 2.1 Loan Agreement. Except as amended hereby, the provisions
of the Loan Agreement shall remain in full force and effect. References in the
Loan Agreement and the other Loan Documents shall be references to the Loan
Agreement as amended by this Amendment.

         Section 2.2 Governing Law. This Amendment shall be governed by and
construed in accordance with the laws of the State of Tennessee without
reference to its choice of law rules.

         Section 2.3 Execution in Counterparts. This Amendment may be executed
in one or more counterparts, each of which shall be considered an original
instrument, but all of which shall be considered one and the same agreement,
and shall become binding when one or more counterparts have been signed by each
of the parties and delivered to each of the parties.

         Section 2.4 Representations. Borrower hereby makes the following
representations and warranties:

                  (a) as of the date hereof, Borrower has no defense against
         payment of any or all of the Obligations;

                  (b) as of the date hereof, no Event of Default or Unmatured
         Default has occurred or is continuing (after giving effect to this
         Amendment).

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         IN WITNESS WHEREOF, the parties hereto have duly executed this
Agreement as of the day and year first above written.

BANK:                                       BORROWER:

U.S BANK NATIONAL ASSOCIATION               ARC OF BELLINGHAM, L.P.,
                                      a Tennessee Limited Partnership

                                         By: Ambulatory Resource
                                         Centres of
                                           Washington, Inc., its General
                                         Partner

BY:
   --------------------------------

     BY:
        --------------------------------

TITLE:
      -----------------------------
     TITLE:
           -----------------------------

     BY:
        --------------------------------

     TITLE:
           -----------------------------

                                      GUARANTOR:

                                      SYMBION AMBULATORY
                                      RESOURCE CENTRES, INC.

BY:
   --------------------------------

TITLE:
      -----------------------------

BY:
   --------------------------------

TITLE:
      -----------------------------

<PAGE>

SYMBION:

The undersigned guarantor of the indebtedness extended pursuant to the Loan
Agreement hereby acknowledges the foregoing amendment.

SYMBION, INC.

BY:
   --------------------------------

TITLE:
      -----------------------------

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