Document:

<PAGE>

                                                                   EXHIBIT 10.17

                                             March 26, 2004

Smithway Motor Xpress, Inc.
2031 Quail Avenue
Fort Dodge, Iowa 50501

And

East West Motor Express, Inc.
1170 JB Drive
Black Hawk, South Dakota 57718

RE:      TENTH AMENDMENT TO AMENDED AND RESTATED LOAN AND
         SECURITY AGREEMENT

Gentlemen:

         SMITHWAY MOTOR XPRESS, INC., an Iowa corporation ("SMITHWAY INC.") and
EAST WEST MOTOR EXPRESS, INC., a South Dakota corporation ("EAST WEST")
(Smithway Inc. and East West each a "BORROWER" and collectively the "BORROWERS")
and LASALLE BANK NATIONAL ASSOCIATION, a national banking association ("LENDER")
have entered into that certain Amended and Restated Loan and Security Agreement
dated December 28, 2001 (the "SECURITY AGREEMENT"). From time to time
thereafter, Borrowers and Lender may have executed various amendments (each an
"AMENDMENT" and collectively the "AMENDMENTS") to the Security Agreement (the
Security Agreement and the Amendments hereinafter are referred to, collectively,
as the "AGREEMENT"). Borrowers and Lender now desire to further amend the
Agreement as provided herein, subject to the terms and conditions hereinafter
set forth.

         NOW, THEREFORE, in consideration of the foregoing recitals, the mutual
covenants and agreements set forth herein and other good and valuable
consideration, the receipt and sufficiency of which are hereby acknowledged, the
parties hereto hereby agree as follows:

<PAGE>

Smithway Motor Xpress, Inc.
March 26,2004
Page 2

         1.       The Agreement hereby is amended as follows:

         (A)      Subparagraph 4(b)(iv) of the Agreement is deleted in its
entirety and the following is substituted in its place:

                  (IV)     AMENDMENT FEE: Borrowers shall pay to Lender an
                           amendment fee of Five Hundred and No/100 Dollars
                           ($500.00), which fee shall be fully earned and
                           payable upon execution of this Amendment.

         (B) Subparagraphs 15(m) and 15(n) of the Agreement are deleted in their
entirety and the following are substituted in their place:

                  (M)      CHANGE OF CONTROL.

                           The failure of Smithway Corp. to own and have voting
                           control of at least one hundred percent (100%) of the
                           issued and outstanding capital stock of each Borrower
                           and the failure of Marlys L. Smith to own and have
                           voting control of at least twenty (20) percent of the
                           issued and outstanding voting Class A and Class B
                           common shares of Smithway Corp.

                  (N)      CHANGE OF MANAGEMENT.

                           If Larry Owens shall cease to be the President and
                           CEO of Smithway Corp. and President of each Borrower
                           at any time.

         2.       This Amendment shall become binding when fully executed by all
parties hereto, and shall be effective March 26, 2004.

         3.       Except as expressly amended hereby and by any other
supplemental documents or instruments executed by either party hereto in order
to effectuate the transactions contemplated hereby, the Agreement hereby is
ratified and confirmed by the parties hereto and remain in full force and effect
in accordance with the terms thereof.

<PAGE>

Smithway Motor Xpress, Inc.
March 26,2004
Page 3

                                             LASALLE BANK NATIONAL ASSOCIATION

                                             By /s/ John Mostofi

                                             Title Senior Vice President

ACKNOWLEDGED AND AGREED TO this 26th day of March, 2004:

SMITHWAY MOTOR XPRESS, INC.

By /s/ G. Larry Owens
   ---------------------------
     G. LARRY OWENS

Title PRESIDENT & CEO

EAST WEST MOTOR EXPRESS, INC.

By /s/ G. Larry Owens
   ---------------------------
      G. LARRY OWENS

Title PRESIDENT & CEO

Consented and agreed to by the following guarantor(s) of the obligations of
SMITHWAY MOTOR XPRESS, INC. and EAST WEST MOTOR EXPRESS, INC. to LASALLE BANK
NATIONAL ASSOCIATION.

SMSD ACQUISITION CORP.

By /s/ G. Larry Owens
   ---------------------------
     G. LARRY OWENS

Title: PRESIDENT & CEO

Date: MARCH 26, 2004

<PAGE>

Smithway Motor Xpress, Inc.
March 26,2004
Page 4

SMITHWAY MOTOR XPRESS CORP.

By /s/ G. Larry Owens
   -----------------------------------------
      G. LARRY OWENS

Title: PRESIDENT & CEO

Date: MARCH 26, 2004
M1:1101422.02<PAGE>

                                                                   EXHIBIT 10.18

                                            April 23, 2004

Smithway Motor Xpress, Inc.
2031 Quail Avenue
Fort Dodge, Iowa 50501

And

East West Motor Express, Inc.
1170 JB Drive
Black Hawk, South Dakota 57718

RE:      ELEVENTH AMENDMENT TO AMENDED AND RESTATED LOAN AND SECURITY AGREEMENT

Gentlemen:

         SMITHWAY MOTOR XPRESS, INC., an Iowa corporation ("SMITHWAY INC.") and
EAST WEST MOTOR EXPRESS, INC., a South Dakota corporation ("EAST WEST")
(Smithway Inc. and East West each a "BORROWER" and collectively the "BORROWERS")
and LASALLE BANK NATIONAL ASSOCIATION, a national banking association ("LENDER")
have entered into that certain Amended and Restated Loan and Security Agreement
dated December 28, 2001 (the "SECURITY AGREEMENT"). From time to time
thereafter, Borrowers and Lender may have executed various amendments (each an
"AMENDMENT" and collectively the "AMENDMENTS") to the Security Agreement (the
Security Agreement and the Amendments hereinafter are referred to, collectively,
as the "AGREEMENT"). Borrowers and Lender now desire to further amend the
Agreement as provided herein, subject to the terms and conditions hereinafter
set forth.

         NOW, THEREFORE, in consideration of the foregoing recitals, the mutual
covenants and agreements set forth herein and other good and valuable
consideration, the receipt and sufficiency of which are hereby acknowledged, the
parties hereto hereby agree as follows:

         1.       The Agreement hereby is amended as follows:

         (A)      Subsection 4(b)(iv) of the Agreement is deleted in its
entirety and the following is substituted in its place:

<PAGE>

SMITHWAY MOTOR XPRESS, INC.
EAST WEST MOTOR EXPRESS, INC.
APRIL 23, 2004
PAGE 2

                  (IV)     ONE-TIME AMENDMENT FEE: Borrowers shall pay to Lender
                           a one-time amendment fee of Five Hundred and No/100
                           Dollars ($500.00), which fee shall be fully earned
                           and payable upon execution of this Amendment.

         (B)      Section 10 of the Agreement is deleted in its entirety and the
following is substituted in its place:

                  10.      TERMINATION: AUTOMATIC RENEWAL.

                           THIS AGREEMENT SHALL BE IN EFFECT UPON EXECUTION OF
                           THIS AMENDMENT UNTIL JANUARY 1, 2006 (THE "ORIGINAL
                           TERM") AND SHALL AUTOMATICALLY RENEW ITSELF FROM
                           MONTH TO MONTH THEREAFTER (EACH SUCH ONE-MONTH
                           RENEWAL BEING REFERRED TO HEREIN AS A "RENEWAL TERM")
                           unless (A) THE DUE DATE OF THE LIABILITIES IS
                           ACCELERATED PURSUANT TO SECTION 16 HEREOF; OR (B) A
                           BORROWER OR LENDER ELECTS TO TERMINATE THIS AGREEMENT
                           EFFECTIVE AT THE END OF THE ORIGINAL TERM OR AT THE
                           END OF ANY RENEWAL TERM BY GIVING THE OTHER PARTY
                           WRITTEN NOTICE OF SUCH ELECTION AT LEAST FIFTEEN (15)
                           DAYS PRIOR TO THE END OF THE ORIGINAL TERM OR THE
                           THEN CURRENT RENEWAL TERM IN WHICH CASE BORROWERS
                           SHALL PAY ALL OF THE LIABILITIES IN FULL ON THE LAST
                           DAY OF SUCH TERM. If one or more of the events
                           specified in clauses (a) and (b) occurs, then (i)
                           Lender shall not make any additional Loans on or
                           after the date identified as the date on which the
                           Liabilities are to be repaid; and (ii) this Agreement
                           shall terminate on the date thereafter that the
                           Liabilities are paid in full. At such time as
                           Borrowers have repaid all of the Liabilities and this
                           Agreement has terminated, Borrowers shall deliver to
                           Lender a release, in form and substance satisfactory
                           to Lender, of all obligations and liabilities of
                           Lender and its officers, directors, employees,
                           agents, parents, subsidiaries and

<PAGE>

SMITHWAY MOTOR XPRESS, INC.
EAST WEST MOTOR EXPRESS, INC.
APRIL 23, 2004
PAGE 3

                           affiliates to such Borrowers, and if Borrowers are
                           obtaining new financing from another lender,
                           Borrowers shall deliver such lender's indemnification
                           of Lender, in form and substance satisfactory to
                           Lender, for checks which Lender has credited to such
                           Borrower's account, but which subsequently are
                           dishonored for any reason or for automatic
                           clearinghouse or wire transfers not yet posted to
                           such Borrower's account.

         2.       This Amendment shall become binding when fully executed by all
parties hereto.

         3.       Except as expressly amended hereby and by any other
supplemental documents or instruments executed by either party hereto in order
to effectuate the transactions contemplated hereby, the Agreement hereby is
ratified and confirmed by the parties hereto and remain in full force and effect
in accordance with the terms thereof.

                                               LASALLE BANK NATIONAL ASSOCIATION

                                               By /s/ John Mostofi
                                                  ------------------------------
                                                Title Senior Vice President

ACKNOWLEDGED AND AGREED TO this 23rd day of April, 2004:

SMITHWAY MOTOR XPRESS, INC.

By  /s/ G. Larry Owens
    -------------------------
       G. LARRY OWENS

Title PRESIDENT & CEO

<PAGE>

SMITHWAY MOTOR XPRESS, INC.
EAST WEST MOTOR EXPRESS, INC.
APRIL 23, 2004
PAGE 4

EAST WEST MOTOR EXPRESS, INC.

By /s/ G. Larry Owens
   ---------------------
       G. LARRY OWENS

Title PRESIDENT & CEO

Consented and agreed to by the following guarantor(s) of the obligations of
SMITHWAY MOTOR XPRESS, INC. and EAST WEST MOTOR EXPRESS, INC. to LASALLE BANK
NATIONAL ASSOCIATION.

SMSD ACQUISITION CORP.

By /s/ G. Larry Owens
   --------------------------
     G. LARRY OWENS

Title: PRESIDENT & CEO

Date: APRIL 23, 2004

SMITHWAY MOTOR XPRESS CORP.

By /s/ G. Larry Owens
   ---------------------------
     G. LARRY OWENS

Title: PRESIDENT & CEO

Date: APRIL 23, 2004
M1:1101424.02

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