Glutathione deficiency, induced in adult mice by administering buthionine sulfoximine (an inhibitor of glutathione synthesis), led to a rapid and substantial increase in ascorbate in the liver. This effect was apparent 2-4 hr after giving the inhibitor; subsequently, the level of ascorbate decreased and that of dehydroascorbate increased markedly, supporting the conclusion that glutathione functions physiologically to keep ascorbate in its reduced form. In kidney and lung also, ascorbate levels decreased, and dehydroascorbate increased. Increased synthesis of ascorbate in glutathione-deficient adult mice seems to protect against tissue damage. In contrast, newborn rats, which (like guinea pigs and humans) apparently do not synthesize ascorbate, suffer severe damage to liver and other organs; previous studies showed that administration of ascorbate prevents such tissue damage. The findings support the view that the antioxidant actions of glutathione and ascorbate are closely linked and involve a mechanism in which decrease of the glutathione level, perhaps associated with an oxidative event, stimulates ascorbate synthesis.