The pollution of the operating room atmosphere with methoxyflurane was discussed. The measurement of methoxyflurane concentration was done by gas chromatography. Sixty cases were examined by utilizing the model-lung with or without air conditioning system. While 49 cases were examined during general anesthesia in the same operating room with or without waste anesthetic gases scavenging system and gas collecting system. As the results, it was showed that air conditioning system decreased the concentration of methoxyflurane to one third of its none-using one, and waste anesthetic gases scavenging system and gas collecting system decreased it more to about one half.