Occupational hazards associated with ethylene-thiourea (96457) are reviewed. NIOSH recommends that ethylene-thiourea be handled in the workplace as though it were a human carcinogen and teratogen. Ethylene-thiourea is a white crystalline solid used as an accelerator in the curing of neoprene and other elastomers. Approximately 3,500 workers may be potentially exposed in the rubber industry. In addition, exposure to ethylene-thiourea results from the widely used ethylene bisdithiocarbamate fungicides. In humans, exposure can cause drying and thickening of the skin, goiter, or other effects related to decreased output of thyroid hormone. Marked teratogenic effects have been demonstrated in laboratory rats. When 50 milligrams per kilogram were applied to the skin of pregnant Sprague-Dawley-rats, malformations were observed in all fetuses. Dose and day of gestation were critical in other studies. Ethylene-thiourea has been shown to cause cancer in Charles-River-CD- rats. Thyroid carcinomas were reported and some solid cell adenomas were seen. Suggested guidelines for minimizing employee exposure to ethylene-thiourea include substitution of less hazardous products, employee isolation, control of the sources of contamination, and the use of personal protective equipment. The last step should not be the only measure used and should be relied on only for brief periods. The authors conclude that occupational exposure should be minimized, being limited to as few employees as possible under the lowest exposure conditions possible. Alternatives should be investigated.