The robotic characterization program at Three Mile Island Unit 2 evolved in response to requirements and problems revealed during earlier work. From October 31 to November 9, 1987, an extensive survey of the 86.1-m (282-ft, 6-in.) elevation of the reactor building (RB) was conducted using the Rover robot and the Diver directional survey system. Personnel obtained 243 contact and general area exposure rates using directional survey instrumentation. From August 19 to August 24, 1988, another survey of the 86.1-m (282-ft, 6-in.) elevation of the RB was conducted. The results of this survey suggest that there was a reduction of the basement source term as the result of decontamination work, but insufficient data had been obtained to properly quantify the effects of the various decontamination efforts. The results of the surveys, and the lessons learned about equipment and survey technique during the robotic characterization program, are reported to enhance understanding of the basement status and to assist in future planning for robotic surveying systems.