In March 1982, the gross decontamination experiment was conducted in the Three Mile Island Unit 2 reactor building (RB). The intent of the experiment was twofold: (a) to determine which of several commonly used decontamination techniques would be the most efficient at reducing contamination levels on vertical and horizontal surfaces and (b) to actually reduce radiation and surface contamination levels in the accessible areas of the RB to reduce person-rem expenditures for future entries. Accessible areas included the entire RB except inside the D-rings, inside the enclosed stairwell, and the 282-ft elevation. The experiment consisted of six separate tasks that were implemented in nine different major work segments (work packages), accomplished during 15 RB entries over a 30-day period. Approximately 0.4 person-Sv was expended in completing the experiment. In spite of operational deviations from the original plan and the lack of emphasis on pre- and posttest data acquisition, the average RB contamination levels dropped by a factor of 10 and the most effective decontamination techniques were determined. Decontamination factors 1 to ∼125 were seen.