SECOND AMENDMENT TO 1997 REVOLVING CREDIT AGREEMENT


         THIS SECOND  AMENDMENT to 1997 REVOLVING  CREDIT AGREEMENT (the "Second
Amendment")  is  intended  to  amend  the  terms of the  1997  Revolving  Credit
Agreement  (the  "Agreement")  dated as of February 26, 1997,  as amended by the
First Amendment to 1997 Revolving Credit Agreement,  dated as of March 31, 1997,
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 in interest 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:

         1.       The maturity  date  referenced in Section 2.1 of the Agreement
                  shall be extended to June 30,  1999.  Every  reference  in the
                  Agreement  to June 30, 1998 shall be changed to June 30, 1999.
                  The maximum maturity date for Converted Notes of June 30, 2002
                  referenced in Section 2.4 of the  Agreement  shall be extended
                  to June 30, 2003.

         2.        Section 4.20 of the Agreement is amended to read as follows:

                   4.20    Acquisitions.  The  Borrower  shall not  acquire  any
                           stock or any equity interest in, or warrants therefor
                           or securities into the same, or a substantial portion
                           of the assets of,  another  entity  without the prior
                           written consent of the Revolving  Lenders;  provided,
                           however, that the Borrower shall be permitted to make
                           on a  cumulative  basis  from and after  July 1, 1997
                           such  acquisitions in an amount not to exceed Fifteen
                           Million  Dollars   ($15,000,000)   in  the  aggregate
                           without the consent of the Revolving  Lenders if such
                           acquisitions are in or from entities which:

                                       (a)  are in the  business  of  electron-
                                    ically  communicating  time-sensitive
                                    information to subscribers;

                                       (b)  have  their  principal  place  of
                                    business  in the  United  States  or
                                    Canada; and

                                       (c) have a positive  operating cash flow,
                                    calculated  in the same method as is used to
                                    calculate the Borrower's Operating Cash Flow
                                    for purposes of this Agreement; and

                                       1

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<PAGE>


                           the   Borrower  or  any   Subsidiary   is  not,   and
                           immediately  after the  making  of such  acquisition,
                           will not be in default  under any other  covenant  or
                           provision  of  this  Agreement  (including,   without
                           limitation,  the covenants and provisions  pertaining
                           to   minimum   net   worth   and    limitations    on
                           indebtedness).

         This Second  Amendment  shall not affect and there  remain  outstanding
from the  Borrower to the Banks,  the  Existing  Term Notes and the Related Bank
Debt.

         This Second 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 SECOND AMENDMENT
TO 1997 REVOLVING CREDIT AGREEMENT dated as of June 30, 1997.


                                               DATA TRANSMISSION NETWORK
                                               CORPORATION



                                               By
                                                 -------------------------------
                                                 Title:

                                       2

                                    - 170 -
<PAGE>







                                               FIRST NATIONAL BANK OF OMAHA



                                               By
                                                 -------------------------------
                                                 Title:






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

                                    - 171 -
<PAGE>


                                               THE SUMITOMO BANK, LIMITED


                                               By
                                                 -------------------------------
                                                 Title:



                                               By
                                                 -------------------------------
                                                 Title:






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

                                    - 172 -
<PAGE>






                                               FIRST NATIONAL BANK, WAHOO,
                                               NEBRASKA



                                               By
                                                 -------------------------------
                                                 Title:






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

                                    - 173 -
<PAGE>


                                               NBD BANK


                                               By
                                                 -------------------------------
                                                 Title:






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

                                    - 174 -
<PAGE>







                                               NORWEST BANK NEBRASKA, N.A.




                                               By
                                                 -------------------------------
                                                 Title:






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

                                    - 175 -
<PAGE>


                                               LASALLE NATIONAL BANK, a national
                                               banking association




                                               By
                                                 -------------------------------
                                                 Title:






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

                                    - 176 -
<PAGE>


                                               MERCANTILE BANK OF
                                               ST. LOUIS, N.A.


                                               By
                                                 -------------------------------
                                                 Title:






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

                                    - 177 -
<PAGE>







                                               FIRST BANK, NATIONAL
                                               ASSOCIATION


                                               By
                                                 -------------------------------
                                                 Title:






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

                                    - 178 -
<PAGE>

                                               NATIONSBANK, N.A.,
                                               Successor in Interest to The
                                               Boatmen's Nat'l Bank of St. Louis



                                               By
                                                 -------------------------------
                                                 Title:






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

                                    - 179 -
<PAGE>


                                               BANK OF MONTREAL,
                                               Chicago Branch




                                               By
                                                 -------------------------------
                                                 Title:






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

                                    - 180 -