The first credible clinical description of peripheral polyneuropathy occurring in man as a result of occupational overexposure to ethylene oxide (EO) vapor was not published until 1979. The relevant information is assessed concerning the occurrence and significance of neuropharmacologic and neurotoxic effects in both experimental mammals and human populations resulting from exposure to EO. A sufficient number of animal studies have been conducted to allow a reasonable assessment of the neurotoxic potential of EO by repeated exposure. A characteristic neurotoxic effect, predominantly peripheral and affecting the lumbosacral nerves, has been induced in several species by repeatedly exposing them to EO vapor. Several studies have shown that repeated exposure of a variety of mammals to EO vapor results in the development of a peripheral neuropathy characterized by paralysis of hind-limb muscles with impairment of sensation and reflexes, and from which recovery occurs.