The reaction of glutathione and ethylene dibromide (EDB) was studied in vitro in the presence of rat liver homogenate. It was found that the release of two bromide ions for EDB required stoichiometric amounts of GSH. S-(beta-hydroxyethyl) glutathione has been identified as the major product formed in vitro. S-S' ethylene bis glutathione was formed in traces. The above two compounds and the sulphoxides of S-(beta-hydroxyethyl) glutathione were identified also in the liver of rats treated with labeled EDB. S-(beta-hydroxyetyl) mercapturic acid was identified in the kidney.