Based on the results of recent tests for mutagenesis, NIOSH recommends that exposure to ethylene oxide be controlled so that workers are not exposed to a concentration greater than 75 ppm determined during a 15 minute sampling period, as a ceiling occupational exposed limit and in addition, with the provision that the time-weighted average concentration limit of 50 ppm for a work day not be exceeded. As additional information on the toxic effect of ethylene oxide becomes available, this recommended level for exposures of short duration may be altered. Where the use of the compound is to be continued, improved techniques of exhausting the gas from the sterilizer, the aerator and the sterilized items need to be implemented. Under such control, the use of ethylene oxide as a medical sterilizant can be continued with less risk to the health of employees. Included is a summary of airborne ethylene oxide concentrations measured within health care facilities as part of a field survey. NIOSH estimates that there are in excess of 10,000 ethylene oxide sterlizers used in U.S. health care facilities, and that approximately 75,000 workers are potentially exposed to the gas in those facilities. Reasons for the unnecessary exposure were found to include poor ventilation of equipment and working spaces, improper handling of sterilized items, untrained workers, poor operating techniques, poorly designed sterilization facilities, and design limitations of the sterilization equipment.