We studied the association between the movement of operating room personnel and bacterial contamination of the operative field during 12 clean operations. Settle plates placed on the patient's chest and instrument table were exposed during the operation. As a control, settle plates were exposed in the same locations when no personnel and patients were in the room. Bacterial contamination of the aseptic field was categorized as disseminating (Group A: greater than 42 combined movements) and nondisseminating (Group B: less than 42 combined movements). There were 24 persons in each group. There was a highly significant difference between the two groups in the colony counts on settling plates. More vigorous movement was associated with increased bacterial contamination of the operative field. Low bacterial colony counts were found in the control plates, ruling out environmental sources of contamination. Bacterial fallout correlated with the movement of personnel. Measures to reduce excessive movement in the OR are recommended.