The distribution of intravenously injected35S-glutathione in male and pregnant mice has been studied by whole body autoradiography. The radioactivity was rapidly accumulated in the liver, renal cortex, pancreas, salivary glands, gastric mucosa and the intestinal mucosa. The uptake of the isotope into brain occurred slowly and the radioactivity at 7 days after injection increased to the same level as that in the skeletal muscle. The radioactivity in the maternal tissues reached highest 3 hours after injection, whereas those in the fetuses increased gradually until 24 hours. Higher accumulation was observed in the bone, liver, eye and the brain of fetus.