THIRD AMENDMENT TO 1997 REVOLVING CREDIT AGREEMENT


         THIS THIRD  AMENDMENT to 1997  REVOLVING  CREDIT  AGREEMENT (the "Third
Amendment")  is  intended  to  amend  the  terms of the  1997  Revolving  Credit
Agreement  (the  "Agreement")  dated as of  February  26,  1997,  as  previously
amended,  among DATA TRANSMISSION  NETWORK  CORPORATION;  FIRST NATIONAL BANK OF
OMAHA;  FIRST NATIONAL  BANK,  WAHOO,  NEBRASKA;  NBD BANK,  N.A.;  NORWEST BANK
NEBRASKA, N.A.; THE SUMITOMO BANK, LIMITED;  MERCANTILE BANK OF ST. LOUIS, N.A.;
FIRST BANK, NATIONAL ASSOCIATION;  BANK OF MONTREAL;  LASALLE NATIONAL BANK; and
NATIONSBANK,  N.A.  (successor to THE BOATMEN'S NATIONAL BANK OF ST. LOUIS). All
terms and  conditions  of the  Agreement  shall  remain in full force and effect
except as expressly amended herein.  All capitalized terms herein shall have the
meanings prescribed in the Agreement. The Agreement shall be amended as follows:

         The parties hereby  acknowledge that,  effective as of the date hereof,
$16,000,000  of the revolving  credit  facility  available to Borrower under the
Agreement  shall be advanced to Borrower  for the purpose of  prepaying  certain
subordinated debt and such advance shall be immediately converted to a term loan
in accordance with Section 2.4 of the Agreement.  Notwithstanding Section 2.5 of
the  Agreement,  such loan  shall  bear  interest  at the fixed rate of 7.5% per
annum.  In Section 2.1 of the Agreement,  the reference to the maximum amount of
revolving  credit  available to be advanced shall be reduced from $33,000,000 to
$17,000,000,  and the references to each Bank's  maximum  advance limit shall be
reduced  accordingly  on a pro rata  basis,  as shown on  Exhibit  A. No further
increases in the Base Revolving  Credit Facility are available to be implemented
under Section 2.1 of the Agreement.

         In   connection   with   this   Third   Amendment   the   Borrower   is
contemporaneously executing and delivering to the Banks Converted Notes dated as
of the date  hereof  in the  respective  principal  amounts  shown on  Exhibit A
hereto.  This Third Amendment shall not affect and there remain outstanding from
the Borrower to the Banks, the Existing Term Notes and the Related Bank Debt.

         This Third Amendment may be executed in several  counterparts  and such
counterparts together shall constitute one and the same instrument.

         Except as expressly  agreed  herein,  all terms of the Agreement  shall
remain in full force and effect.

         IN WITNESS WHEREOF,  the undersigned have executed this THIRD AMENDMENT
TO 1997 REVOLVING CREDIT AGREEMENT dated as of March 16, 1998.

                                       1
                                    - 444 -
<PAGE>


                                      DATA TRANSMISSION NETWORK CORPORATION



                                      By /s/ Brian L. Larson
                                        -------------------------------
                                        Title:Vice President, CFO & Secretary

                                       2
                                    - 445 -
<PAGE>

                                      FIRST NATIONAL BANK OF OMAHA



                                      By /s/ James P. Bonham
                                        -------------------------------
                                        Title:Vice President






NOTICE: A credit  agreement must be in writing to be enforceable  under Nebraska
law. To protect you and us from any  misunderstandings  or disappointments,  any
contract,  promise,  undertaking,  or offer to forebear repayment of money or to
make any other financial  accommodation in connection with this loan of money or
grant or extension of credit,  or any amendment of,  cancellation of, waiver of,
or  substitution  for any or all of the terms or provisions of any instrument or
document executed in connection with this loan of money or grant or extension of
credit, must be in writing to be effective.

                                      INITIALED:


                                      Borrower


                                       3
                                    - 446 -
<PAGE>





                                      THE SUMITOMO BANK, LIMITED


                                      By /s/ Michael F. Murphy
                                        -------------------------------
                                        Title:Vice President and Manager


                                      By /s/ Teresa A. Lekich
                                        -------------------------------  
                                        Title:Vice President







NOTICE: A credit  agreement must be in writing to be enforceable  under Nebraska
law. To protect you and us from any  misunderstandings  or disappointments,  any
contract,  promise,  undertaking,  or offer to forebear repayment of money or to
make any other financial  accommodation in connection with this loan of money or
grant or extension of credit,  or any amendment of,  cancellation of, waiver of,
or  substitution  for any or all of the terms or provisions of any instrument or
document executed in connection with this loan of money or grant or extension of
credit, must be in writing to be effective.

                                      INITIALED:


                                      Borrower


                                       4
                                    - 447 -
<PAGE>



                                      FIRST NATIONAL BANK, WAHOO,
                                      NEBRASKA



                                      By /s/ Elizabeth Rezac
                                        ------------------------------
                                        Title Second Vice President




NOTICE: A credit  agreement must be in writing to be enforceable  under Nebraska
law. To protect you and us from any  misunderstandings  or disappointments,  any
contract,  promise,  undertaking,  or offer to forebear repayment of money or to
make any other financial  accommodation in connection with this loan of money or
grant or extension of credit,  or any amendment of,  cancellation of, waiver of,
or  substitution  for any or all of the terms or provisions of any instrument or
document executed in connection with this loan of money or grant or extension of
credit, must be in writing to be effective.

                                      INITIALED:


                                      Borrower


                                       5
                                    - 448 -
<PAGE>





                                      NBD BANK


                                      By Nathan L. Bloch
                                        ----------------------------- 
                                        Title:First Vice President





NOTICE: A credit  agreement must be in writing to be enforceable  under Nebraska
law. To protect you and us from any  misunderstandings  or disappointments,  any
contract,  promise,  undertaking,  or offer to forebear repayment of money or to
make any other financial  accommodation in connection with this loan of money or
grant or extension of credit,  or any amendment of,  cancellation of, waiver of,
or  substitution  for any or all of the terms or provisions of any instrument or
document executed in connection with this loan of money or grant or extension of
credit, must be in writing to be effective.

                                      INITIALED:


                                      Borrower


                                       6
                                    - 449 -
<PAGE>




                                      NORWEST BANK NEBRASKA, N.A.




                                      By /s/ Kevin Munro
                                        -------------------------------
                                        Title: Vice President




NOTICE: A credit  agreement must be in writing to be enforceable  under Nebraska
law. To protect you and us from any  misunderstandings  or disappointments,  any
contract,  promise,  undertaking,  or offer to forebear repayment of money or to
make any other financial  accommodation in connection with this loan of money or
grant or extension of credit,  or any amendment of,  cancellation of, waiver of,
or  substitution  for any or all of the terms or provisions of any instrument or
document executed in connection with this loan of money or grant or extension of
credit, must be in writing to be effective.

                                      INITIALED:


                                      Borrower


                                       7
                                    - 450 -
<PAGE>





                                      LASALLE NATIONAL BANK, a national
                                      banking association




                                      By /s/ Tom Harmon
                                        -------------------------------
                                        Title:Assistant Vice President





NOTICE: A credit  agreement must be in writing to be enforceable  under Nebraska
law. To protect you and us from any  misunderstandings  or disappointments,  any
contract,  promise,  undertaking,  or offer to forebear repayment of money or to
make any other financial  accommodation in connection with this loan of money or
grant or extension of credit,  or any amendment of,  cancellation of, waiver of,
or  substitution  for any or all of the terms or provisions of any instrument or
document executed in connection with this loan of money or grant or extension of
credit, must be in writing to be effective.

                                      INITIALED:


                                      Borrower


                                       8
                                    - 451 -
<PAGE>






                                      MERCANTILE BANK OF
                                      ST. LOUIS, N.A.


                                      By Joseph L. Sooter, Jr.
                                        -------------------------------
                                        Title: Vice President





NOTICE: A credit  agreement must be in writing to be enforceable  under Nebraska
law. To protect you and us from any  misunderstandings  or disappointments,  any
contract,  promise,  undertaking,  or offer to forebear repayment of money or to
make any other financial  accommodation in connection with this loan of money or
grant or extension of credit,  or any amendment of,  cancellation of, waiver of,
or  substitution  for any or all of the terms or provisions of any instrument or
document executed in connection with this loan of money or grant or extension of
credit, must be in writing to be effective.

                                      INITIALED:


                                      Borrower


                                       9
                                    - 452 -
<PAGE>





                                      FIRST BANK, NATIONAL
                                      ASSOCIATION


                                      By /s/ Beth Morgan
                                        ----------------------------------
                                        Title: Vice President




NOTICE: A credit  agreement must be in writing to be enforceable  under Nebraska
law. To protect you and us from any  misunderstandings  or disappointments,  any
contract,  promise,  undertaking,  or offer to forebear repayment of money or to
make any other financial  accommodation in connection with this loan of money or
grant or extension of credit,  or any amendment of,  cancellation of, waiver of,
or  substitution  for any or all of the terms or provisions of any instrument or
document executed in connection with this loan of money or grant or extension of
credit, must be in writing to be effective.

                                      INITIALED:


                                      Borrower


                                       10
                                    - 453 -
<PAGE>




                              NATIONSBANK,   N.A.  (successor  in  interest  to
                              THE BOATMEN'S NATIONAL BANK
                              OF ST. LOUIS



                              By /s/ Roger Bettlach
                                ---------------------------------------
                                Title: Assistant Vice President






NOTICE: A credit  agreement must be in writing to be enforceable  under Nebraska
law. To protect you and us from any  misunderstandings  or disappointments,  any
contract,  promise,  undertaking,  or offer to forebear repayment of money or to
make any other financial  accommodation in connection with this loan of money or
grant or extension of credit,  or any amendment of,  cancellation of, waiver of,
or  substitution  for any or all of the terms or provisions of any instrument or
document executed in connection with this loan of money or grant or extension of
credit, must be in writing to be effective.

                              INITIALED:


                              Borrower

                                       11
                                    - 454 -
<PAGE>




                                      BANK OF MONTREAL, a Canadian bank




                                      By /s/ Kevin Cullen
                                        ---------------------------------
               `                        Title: Associate






NOTICE: A credit  agreement must be in writing to be enforceable  under Nebraska
law. To protect you and us from any  misunderstandings  or disappointments,  any
contract,  promise,  undertaking,  or offer to forebear repayment of money or to
make any other financial  accommodation in connection with this loan of money or
grant or extension of credit,  or any amendment of,  cancellation of, waiver of,
or  substitution  for any or all of the terms or provisions of any instrument or
document executed in connection with this loan of money or grant or extension of
credit, must be in writing to be effective.

                                      INITIALED:


                                      Borrower


                                       12
                                    - 455 -
<PAGE>



                                    Exhibit A
                                       to
                               THIRD AMENDMENT TO
                         1997 REVOLVING CREDIT AGREEMENT


            Maximum Amount
<TABLE>
<CAPTION>

                                               Current Revolving                Available Under
    Bank            Pro Rata %                 Revolving Facility             Revolving Facility*
<S>                 <C>                        <C>                               <C>        
FNB-O               20.7%                      $ 6,831,000                       $ 3,519,000
FNB-W                 .5%                          165,000                            85,000
NBD                 11.9%                        3,927,000                         2,023,000
Norwest              4.8 %                       1,584,000                           816,000
LaSalle             19.9%                        6,567,000                         3,383,000
Sumitomo            10.0%                        3,300,000                         1,700,000
Mercantile          10.3%                        3,399,000                         1,751,000
Montreal            11.6%                        3,828,000                         1,972,000
First Bank          10.3%                        3,399,000                         1,751,000
                                               ---------------------------------------------

                                               $33,000,000                       $17,000,000



*Includes current amounts, if any,  outstanding after Conversion

                                       13
                                    - 456 -
</TABLE>