The metabolism of ethylene dibromide (EDB) has been studied after administration of this compound to rats by stomach tube. N-acetyl-S-(beta-hydroxyethyl) cysteine was isolated from the urine of EDB-dosed rats. The identity of this compound with synthetic N-acetyl-S-(beta-hydroxyethyl) cysteine was proved by chromatographic and electrophoretic methods and by identification of the products obtained by acid and alkaline hydrolysis, by enzymatic hydrolysis and oxidation to a sulfoxide. The second metabolite found in the urine in small amounts was proved to be identical with synthetic S-(beta-hydroxethyl) cysteine. The products of hydrolysis and oxidation from the two compounds were shown by chromatography to be the same. The symmetric S-S'-ethylene-bis-(N-acetyl) cysteine has not been found in the urine of EDB-treated rats. When ethylene or ethylene bromohydrin was administered to rats, the same metabolites were detected in the urine as after EDB poisoning.