EXHIBIT 10.18

                       Lumbermens Mutual Casualty Company

                               September 29, 2003

SeaBright Insurance Holdings, Inc.
SeaBright Insurance Company
2101 4th Avenue, Suite 1600
Seattle, Washington  98121

Ladies and Gentlemen:

            Reference is hereby made to that certain Purchase Agreement (as
amended, the "Purchase Agreement"), dated as of July 14, 2003, by and among
SeaBright Insurance Holdings, Inc., a Delaware corporation (formerly known as
Insurance Holdings, Inc., "Buyer"), Kemper Employers Group, Inc., a Washington
corporation ("KEG"), Lumbermens Mutual Casualty Company, an Illinois domiciled
mutual insurance company ("LMC"), Eagle Pacific Insurance Company, a Washington
domiciled insurance company ("Eagle Pacific"), and Pacific Eagle Insurance
Company, a California domiciled insurance company ("Pacific Eagle" and, together
with KEG, LMC and Eagle Pacific, the "Sellers"), as amended by that certain
letter agreement, dated as of July 30, 2003 (the "July 30 Letter"), and that
certain letter agreement, dated as of September 15, 2003. Capitalized terms used
but not defined herein shall have the respective meanings ascribed to them in
the Purchase Agreement.

            In connection with the Purchase Agreement, Buyer and Sellers hereby
            agree that:

1.    Section 8.2(b) of the Purchase Agreement shall be amended and restated to
      read in its entirety as follows:

      (b) On or prior to the Closing Date, Buyer shall arrange for the
      establishment by Kemper Employers Insurance Company of a defined
      contribution plan under Section 401(k) of the Code (the "KEIC 401(k)
      Plan"). Within two business days following the Closing, Sellers shall
      cause the trustee of the Eagle Employees Savings and Profit Sharing Plan
      (the "Eagle 401(k) Plan") to transfer in cash (but including promissory
      notes evidencing participant loans) to the KEIC 401(k) Plan the account
      balances of the Transferred Employees. Such transfer of account balances
      shall be in accordance with Section 414(l) of the Code.

2.    The reference to "Buyer's 401(k) Plan" in Section 8.2(a) of the Purchase
      Agreement is hereby amended to read as follows: "KEIC's 401(k) Plan".

3.    In order to clarify the intent of the parties at the time of the execution
      of the Purchase Agreement and the July 30 Letter, the definition of KEIC
      Book Value in the Purchase Agreement shall be amended and restated to read
      in its entirety as follows:

      "KEIC Book Value" means an amount equal to the book value of KEIC as of
      the close of business on the day prior to the Closing Date, calculated in
      accordance with the Agreed Accounting Principles, after giving effect to
      the Commutation Agreement, and increased (without duplication) by the
      aggregate amount of (i) the California Prepayments



      transferred by LMC to KEIC pursuant to Section 7.11, (ii) the non-admitted
      prepaid unallocated loss adjustment expense asset resulting from Sellers'
      agreement to be responsible for the servicing of claims under all
      insurance policies written by KEIC prior to the Closing Date and the
      prepayment therefor, regardless of whether such prepayments would
      otherwise be included in calculating book value in accordance with SAP and
      (iii) the net aggregate unrealized gain, if any, as of the close of
      business on the day prior to the Closing Date (net of Taxes) with respect
      to the assets owned by KEIC that are then held on deposit with any
      Administrative Authority.

4.    Notwithstanding anything to the contrary contained in the Purchase
      Agreement, the Commutation Agreement shall be executed by both of LMC and
      KEIC, and the transactions contemplated thereunder shall be consummated,
      immediately following the sale of shares of KEIC by KEG to Buyer, and each
      of Buyer and the Sellers agrees to cause such execution and delivery of
      the Commutation Agreement and the consummation of such transactions to
      occur as of such time. The parties acknowledge that the Commutation
      Agreement is an integral component of the transactions contemplated by the
      Purchase Agreement, and each of Buyer and the Sellers shall report and
      file all Tax Returns on the basis that the transactions occurring under
      the Commutation Agreement are for the account of, and included entirely
      within, LMC's consolidated Tax Return, and no party shall take any
      position inconsistent with the foregoing; provided, however, that
      notwithstanding anything to the contrary in the Purchase Agreement, Buyer
      shall indemnify and hold harmless each of the Seller Group Members from
      and against any and all Losses and Expenses incurred by such Seller Group
      Members in connection with any dispute or other proceeding, if any,
      arising as a result of reporting the transactions on such basis.

5.    Section 7 of the July 30 Letter shall be amended and restated to read in
      its entirety as follows:

      Buyer shall have the right to purchase its own Oracle software licenses
      after the Closing, in lieu of assuming any obligations with respect to any
      of Seller's Oracle software licenses. Buyer shall notify Sellers of its
      decision in this regard within five business days following the Closing.

6.    At the Closing, in lieu of entering into the form of Reinsurance Trust
      Agreement contemplated by the Purchase Agreement and July 30 Letter, LMC
      and KEIC shall enter into the Trust Agreement in the form attached hereto
      as Exhibit A (the "Interim Trust Agreement") with The Bank of New York, as
      trustee. Following the Closing, LMC and Buyer shall use their reasonable
      best efforts to cause as soon as reasonably practicable the amendment and
      restatement of the Interim Trust Agreement to conform to the form of
      Reinsurance Trust Agreement contemplated by the Purchase Agreement and
      July 30 Letter, with such changes as may be requested by The Bank of New
      York and reasonably agreed to by LMC and Buyer; provided, that LMC and
      Buyer shall use their reasonable best efforts to minimize such changes
      from the contemplated form. In the event that LMC and Buyer cannot
      reasonably agree to all of the proposed changes requested by The Bank of
      New York (or such proposed changes materially alter the underlying
      agreement of Buyer and the Sellers with respect to the reinsurance trust
      arrangement), LMC and Buyer agree to use their reasonable best efforts to,
      as soon as reasonably practicable, (i)

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      identify a successor trustee reasonably acceptable to both LMC and Buyer
      and to whom the form of Reinsurance Trust Agreement is acceptable, with
      such changes as may be requested by such successor trustee and reasonably
      agreed to by LMC and Buyer (the "Agreed Trust Agreement"), and (ii) cause
      such Person to succeed to The Bank of New York as trustee of the
      reinsurance trust created pursuant to the Interim Trust Agreement
      simultaneously with an amendment and restatement of the Interim Trust
      Agreement to conform to the form of the Agreed Trust Agreement.

7.    Except as expressly amended by this letter agreement, the Purchase
      Agreement is not otherwise amended or modified and remains in full force
      and effect in accordance with its original terms (as previously amended in
      writing prior to the date of this letter agreement).

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      In witness whereof, each of the parties has caused this letter to be
executed as of the date first written above.

                                SEABRIGHT INSURANCE
                                HOLDINGS, INC.

                                By:      /s/ John G. Pasqualetto
                                    --------------------------------------------
                                    Name: John G. Pasqualetto
                                    Title: President

                                KEMPER EMPLOYERS GROUP, INC.

                                By:      /s/ William A. Hickey
                                    --------------------------------------------
                                    Name: William A. Hickey
                                    Title: Vice President

                                LUMBERMENS MUTUAL CASUALTY COMPANY

                                By:      /s/ William A. Hickey
                                    --------------------------------------------
                                    Name: William A. Hickey
                                    Title: Chief Financial Officer and
                                           Executive Vice President

                                EAGLE PACIFIC INSURANCE COMPANY

                                By:      /s/ John K. Conway
                                    --------------------------------------------
                                    Name: John K. Conway
                                    Title: Secretary

                                PACIFIC EAGLE INSURANCE COMPANY

                                By:      /s/ John K. Conway
                                    --------------------------------------------
                                    Name: John K. Conway
                                    Title: Secretary

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