S. epidermidis and Acinetobacter caused contamination in the central operation theater of Okayama University Hospital in May '78. The Acinetobacter contamination was caused by the detergent 'Nikkol' which was added to 1% Hibitane (Chlorhexidine) solution to make bubbles during hand washing. Hibitane had no effect on Acinetobacter and 'Nikkol', at a concentration of 1%, helped bacterial growth. An investigation of various disinfectants revealed that an iodine preparation (Poridone-iodine) and Vista 300 were effective in preventing bacterial growth. Hibitane was replaced with Poridone-iodine and contamination was no longer a problem. S. epidermidis and other air-born bacteria were brought in by carriers who included doctors and nurses from outside of the operation theater. Installation of UV lamps in the sanitary hall of the operation room reduced the number of air-born bacteria. To avoid contamination, routine microbial examination of the facilities, rearrangement of the sanitary zone and the installation of air-showers is planned.