On September 23, 1993, approximately 1515 central daylight time, a Pitts S1-T, N7FD, and a Pitts S2B, N15AV, collided during taxi at Grayson County Airport, Sherman, Texas. Neither of the pilots were injured and both aircraft sustained substantial damage. Visual meteorological conditions prevailed and no flight plans were filed. Both aircraft were participating in the United States National Aerobatics Championships. N7FD was taxiing for takeoff and N15AV was taxiing inbound following landing. The area where the collision occurred is a 75 foot wide taxiway which runs parallel to runway 17/35. N7FD was north bound and N15AV was south bound. A temporary control tower was in operation at the time of the collision and available information is that both aircraft were cleared to taxi and were instructed to monitor tower. By letter of agreement, the temporary tower was not responsible for monitoring taxi operations.