A central vacuum scavenger modified by the authors, was used to control the atmospheric contamination of the operating room by anesthetic gases and vapours. Air pollution was monitored by measuring the concentrations of halothane vapour in the air of the operating room with the gas chromatograph. Under endotrachal intubation, the semi-colsed circle absorber system was used for anesthetic administration and maintained with 0.8~1.2% Halothane. Total gas flow rates were 4 liter/min with 50% oxygen in nitrous oxide for daily work. Air sampling was taken early in the morning at 10cm high from the floor before anesthesia. After daily work, they were also done at 10cm, 120cm, and 140cm high from the floor and at the corridor of the operating room. We investigated the differences of halothane concentration according to each sits by the changing central vacuum pressure. Results are followings: The atmospheric halothane concentration of the operating room before anesthesia were 0.27±0.12, 0.22±0.11 and 0.15±0.06 ppm.The atmospheric halothane concentration of the operating room after daily work were 7.94 ± 1.30 ppm without the active central vacuum pressure.The atmospheric halothane concentration of the operating room after daily work were 1.41 ±0.48ppm of 20mmHg of central vacuum pressure.The tmospheric halothane concentration of the operating room after daily work were 0.49±0.18ppm of 40mmHg of central vacuum pressure. The atmospheric halothane concentrations at the corridor of the operating room after daily work were 1.09±0.19, 0.77±0.11n and 0.36±0.17ppm when each vacuum pressure was 0mmHg, 20mmHg and 40mmHg. A significant reduction (p<0.01) in atmospheric halothane concentration of the operation room was obtained by the use of the central vacuum pressure with the scavenger. The higher the vacuum pressure, the greater reduction of the operating room air pollution was observed.