Recent research on harmful effects of exposure to ethylene-oxide (75218) (EtO) was reviewed. Approximately 75,000 workers in the health care field have been potentially exposed either through the use of EtO in making medical products or secondarily through the use of EtO gas for sterilization of hospital equipment. In the vicinity of malfunctioning or improperly designed equipment, NIOSH investigations have determined the concentrations of EtO to be in the range of hundreds of parts per million for brief periods. EtO binds to DNA, causing mutations and chromosomal damage. Studies have also delineated the toxic effects of EtO on the reproductive function in both sexes of experimental animals, primarily through an induction of dominant lethal mutations. Carcinogenic properties have been demonstrated in chronic inhalation bioassay studies, and through the intragastric administration of EtO. In case studies of workers, reported incidences of leukemia, stomach cancer, and diseases of the circulatory system have been indicated. Neurological effects in both animals and men have been noted including impairment of sensory and motor functions and muscle atrophy. NIOSH recommends that a worker not be exposed to more than 5 parts per million EtO for more than 10 minutes in any working day, and that the time weighted average 8 hour exposure be less than 0.1 part per million.