The relative importance of various ethylene-oxide (75218) (EtO) emission sources associated with gas sterilizers was assessed and the effectiveness of certain control measures on limiting health care worker exposure to EtO was determined. Nine systems used to control exposures to EtO in hospitals were examined at eight institutions. There were three major sources of emissions in each of the hospitals. Most of the EtO gas mixture was released to the indoor atmosphere at the air gap located at the connection of the drain to the outlet of the water sealed vacuum pump. The opening of the sterilizer door at the completion of the sterilization cycle can result in a very short high exposure to the operator, followed by an increase in the workroom EtO concentration. The load transfer procedure provides the closest contact with EtO for the sterilizer operator. In all but one of the hospitals surveyed, short term exposures were controlled to less than 2 parts per million (ppm) and full shift exposures to less than 0.1ppm. The composition and size of the sterilized load, the location of the sterilizer and the time constraints on sterilization, the type of sterilizer and the types of controls selected, and the level to which EtO exposures are to be controlled all affect the level or extent of control needed by a hospital. In chamber aeration is the best means of control. The next most effective techniques include cycle modifications, local ventilation above the sterilizer door, and a ventilated enclosure around the sterilizer drain. General ventilation did not seem to be as crucial as other types of control techniques.