The pilot of the tailwheel equipped Pitts reported that he had departed from runway 3, flew out to the aerobatic practice box, completed his practice, and returned to the airport. He added that, he entered a downwind for runway 3, and announced his location relative to the traffic pattern throughout the landing. He heard another aircraft making calls in the traffic pattern but nothing he was concerned about. After he landed, during the rollout, about midfield, he heard someone announce on the radio that there was an airplane on the runway. This was the last thing the pilot remembered prior to the impact with the S600. The pilot of the tailwheel equipped S600 reported that while he was en route to the designated aerobatic box, he decided that he needed to return to the airport and land. He added that because the winds were calm he elected to land on runway 21. He made a right base call and did not hear anyone else on the radio. He touched down about 300-500 ft down the runway about 75 miles per hour. He further reported that the impact with the Pitts came without warning. According to the Federal Aviation Administration (FAA) Inspector the pilot of the S600 had taken off from runway 3 en route to the practice box. While en route, the pilot noticed a loose water bottle inside the cockpit and returned to the airport to drop it off. The pilot flew a tight right steep approach for runway 21. The inspector noted that all the S600 radio traffic calls were for runway 3. During the landing roll the two airplanes collided. A postaccident examination revealed substantial damage to both airplanes. Both pilots reported that there were no preaccident mechanical failures or malfunctions with the airplane that would have precluded normal operation.