MODIFICATION AGREEMENT



         BY THIS MODIFICATION AGREEMENT (the "Agreement'), made and entered into
as of the 15th day of May, 1997,  WELLS FARGO BANK, N.A., as successor by merger
to FIRST INTERSTATE BANK OF ARIZONA,  N.A.  (hereinafter  called "Lender"),  and
KNIGHT  TRANSPORTATION,   INC.,  an  Arizona  corporation   (hereinafter  called
"Company") and QUAD K LEASING,  INC., an Arizona  corporation (with the Company,
the "Borrower"),  a wholly owned subsidiary of the Company,  in consideration of
the mutual covenants herein contained and other good and valuable consideration,
the receipt and sufficiency of which is hereby acknowledged,  hereby confirm and
agree as follows:

SECTION 1.  RECITALS.

         1.1 Borrower and Lender  entered into a Loan  Agreement  dated April 1,
1996 (the "Loan Agreement"), which provided for, among other things, a revolving
line of credit  (the  "RLC") in the  amount of  $15,000,000.00,  evidenced  by a
Revolving Promissory Note dated April 1, 1996 executed by the Borrower (the "RLC
Note"),  all upon the terms and  conditions  contained  therein.  All  undefined
capitalized  terms used  herein  shall have the  meaning  given them in the Loan
Agreement. The Loan Agreement, the RLC Note and all other agreements,  documents
and instruments relating to the RLC are referred to as the Loan Documents.

         1.2 As of the date  hereof,  prior to the  effect of the  modifications
contained herein, the outstanding principal balance of the RLC is $0.00.

         1.3  Borrower  and Lender  desire to modify the Loan  Documents  as set
forth herein.

SECTION 2.  LOAN AGREEMENT.

         2.1 The following  definitions in Section 2.1 of the Loan Agreement are
hereby amended to read as follows:

         "LIBOR Rate" means:

                  (a) As to a LIBOR Rate RLC Advance, an interest rate per annum
         equal to sixty-two  and one-half  basis points (62.5 b.p.) in excess of
         the LIBOR Base Rate, rounded upward, if necessary,  to the nearest 1/16
         of 1%, or

                  (b) As to a LIBOR Rate Term Loan,  an interest  rate per annum
         equal to  seventy-five  basis points (75.0 b.p.) in excess of the LIBOR
         Base Rate, rounded upward, if necessary, to the 1/16 of 1%.

                                 Exhibit 10.4.1

         "RLC Commitment Amount" means $10,000,000.00.

         "RLC Maturity Date" means May 15, 1998.

         "RLC Unused Fee" means one-sixteenth of one percent (1/16%).

         2.2 The RLC Note is hereby  amended  to  evidence  the  decreased  loan
amount from  $15,000,000.00  to an amount equal to the RLC Commitment  Amount as
hereby amended.

SECTION 3.  OTHER MODIFICATIONS, RATIFICATIONS AND AGREEMENTS.

         3.1 All  references  to the Loan  Agreement in the Loan  Documents  are
hereby amended to refer to the Loan Agreement as hereby amended.

         3.2 Borrower  acknowledges  that the indebtedness  evidenced by the RLC
Note is just and  owing,  that the  balance  thereof is  correctly  shown in the
records  of  Lender  as of the  date  hereof,  and  Borrower  agrees  to pay the
indebtedness evidenced by the RLC Note according to the terms thereof, as herein
modified.

         3.3 Borrower  hereby  reaffirms to Lender each of the  representations,
warranties,  covenants and  agreements of Borrower set forth in the RLC Note and
the Loan  Agreement,  with the same force and effect as if each were  separately
stated herein and made as of the date hereof.

         3.4 Borrower hereby ratifies, reaffirms,  acknowledges, and agrees that
the  RLC  Note  and  the  Loan  Agreement,   represent  valid,  enforceable  and
collectible  obligations  of  Borrower,  and that there are no existing  claims,
defenses,  personal or otherwise, or rights of setoff whatsoever with respect to
any of these documents or instruments.  In addition,  Borrower hereby  expressly
waives,  releases and absolutely and forever  discharges  Lender and its present
and former shareholders,  directors,  officers,  employees and agents, and their
separate and respective heirs, personal representatives, successors and assigns,
from any and all liabilities,  claims,  demands,  damages,  action and causes of
action,  whether  known or unknown  and  whether  contingent  or  matured,  that
Borrower  may now  have,  or has had  prior  to the  date  hereof,  or that  may
hereafter arise with respect to acts, omissions or events occurring prior to the
date hereof and, without limiting the generality of the foregoing,  from any and
all liabilities,  claims, demands,  damages, actions and causes of action, known
or unknown, contingent or matured, arising out of, or in any way connected with,
the RLC. Borrower further acknowledges and represents that no event has occurred
and no condition  exists that,  after  notice or lapse of time,  or both,  would
constitute a default under this Agreement, the RLC Note or the Loan Agreement.

         3.5 All terms,  conditions  and provisions of the RLC Note and the Loan
Agreement are continued in full force and effect and shall remain unaffected and
unchanged except as specifically
                                       -2-

amended  hereby.  The RLC Note and the Loan Agreement,  as amended  hereby,  are
hereby   ratified  and  reaffirmed  by  Borrower,   and  Borrower   specifically
acknowledges the validity and enforceability thereof.

SECTION 4.  GENERAL.

         4.1 This  Agreement  in no way acts as a release or  relinquishment  of
those  rights  securing  payment of the RLC.  Such  rights are hereby  ratified,
confirmed, renewed and extended by Borrower in all respects.

         4.2 The modifications contained herein shall not be binding upon Lender
until Lender shall have received all of the following:
                                                        
                  (a) An  original  of  this  Agreement  fully  executed  by the
         Borrower.

                  (b)  Such  resolutions  or   authorizations   and  such  other
         documents  as Lender may  require  relating to the  existence  and good
         standing of the Borrower and the authority of any person executing this
         Agreement or other documents on behalf of the Borrower.

         4.3 Borrower shall execute and deliver such additional documents and do
such other acts as Lender may reasonably  require to fully  implement the intent
of this Agreement.

         4.4  Borrower  shall  pay all costs and  expenses,  including,  but not
limited  to,  reasonable  attorneys'  fees  incurred  by  Lender  in  connection
herewith,  whether or not all of the conditions described in Paragraph 4.2 above
are satisfied.  Lender, at its option,  but without any obligation to do so, may
advance funds to pay any such costs and expenses that are the  obligation of the
Borrower,  and all such funds  advanced  shall bear interest at the highest rate
provided in the RLC Note and shall be due and payable upon demand.

         4.5 Notwithstanding anything to the contrary contained herein or in any
other  instrument  executed  by Borrower  or Lender,  or in any other  action or
conduct  undertaken  by  Borrower  or Lender on or before the date  hereof,  the
agreements,  covenants and provisions contained herein shall constitute the only
evidence  of  Lender's  consent to modify the terms and  provisions  of the Loan
Agreement.   Accordingly,   no  express  or  implied   consent  to  any  further
modifications  involving  any of the  matters  set  forth in this  Agreement  or
otherwise shall be inferred or implied by Lender's  execution of this Agreement.
Further,  Lender's  execution of this  Agreement  shall not  constitute a waiver
(either express or implied) of the requirement that any further  modification of
the RLC or of the RLC Note or the Loan  Agreement,  shall  require  the  express
written  approval of Lender;  no such approval  (either  express or implied) has
been given as of the date hereof.
                                       -3-

         4.6 Time is hereby  declared to be of the essence hereof of the RLC, of
the RLC Note and of the Loan Agreement, and Lender requires, and Borrower agrees
to, strict  performance  of each and every  covenant,  condition,  provision and
agreement hereof, of the RLC Note and the Loan Agreement.

         4.7 This  Agreement  shall be  binding  upon,  and  shall  inure to the
benefit  of, the  parties  hereto  and their  heirs,  personal  representatives,
successors and assigns.

         4.8 This  Agreement is made for the sole  protection and benefit of the
parties  hereto,  and no other  person or entity  shall have any right of action
hereon.

         4.9 This Agreement shall be governed by and construed  according to the
laws of the State of Arizona.

         IN  WITNESS  WHEREOF,  these  presents  are  executed  as of  the  date
indicated above.

                                        KNIGHT TRANSPORTATION, INC., an
                                        Arizona corporation



                                        By:       /s/  Randy Knight
                                           -------------------------------------
                                        Name:  Randy Knight
                                             -----------------------------------
                                        Its:       Chairman
                                            ------------------------------------


                                        QUAD-K LEASING, INC,, an Arizona
                                        corporation



                                        By:        /s/ Kevin P. Knight
                                           -------------------------------------
                                        Name:   Kevin P. Knight
                                             -----------------------------------
                                        Its:   President
                                            ------------------------------------

                                                                        BORROWER
                                       -4-

                                        WELLS FARGO BANK,  N.A., as successor by
                                        merger  to  FIRST   INTERSTATE  BANK  OF
                                        ARIZONA, N.A.



                                        By:
                                           -------------------------------------
                                        Name:
                                             -----------------------------------
                                        Its:
                                            ------------------------------------

                                                                          LENDER
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