The relationships between the excretion of xenobiotics in bile as glutathione S-conjugates and in urine as mercapturic acids have been investigated in the rat using three compounds, naphthalene, 1-chloro-2,4- dinitrobenzene and bromsulphthalein. These three compounds have been shown to be excreted in the bile of rats as the respective glutathione S-derivatives following intravenous administration of the parent xenobiotic. Following intraduodenal administration of the radiolabelled glutathione S-conjugates of naphthalene and 1-chloro-2,4-dinitrobenzene, radioactive metabolites were absorbed from the gastrointestinal tract and excreted in urine, especially, and in bile, principally as the corresponding mercapturic acids. Absorption and biliary excretion of material derived from the infused glutathione conjugates was observed to be rapid. A very low absorption and excretion of metabolites derived from bromsulphthaleinglutathione was observed i.e. metabolites of bromsulphthalein showed negligible enterohepatic circulation.