The present study reports data on absorption of orally administered glutathione (GSH) in rat jejunum and in other organs, and the possible role of specific transport systems of GSH and gamma-glutamyltranspeptidase (EC 2.3.2.1; gamma-GT) activity. GSH levels were measured simultaneously in various organs after oral GSH administration to untreated rats and rats treated with L-buthionine sulfoximine (BSO) or acivicin (AT125). BSO selectively inhibits GSH intracellular synthesis and AT125 is a specific inhibitor of gamma-GT activity. GSH levels were also measured after oral administration of an equivalent amount of the constituent amino acids of GSH to untreated and BSO-treated rats. Significant increases in GSH levels were found in jejunum, lung, heart, liver and brain after oral GSH administration to untreated rats. GSH increases were also obtained in all organs, except liver, when GSH was administered to rats previously GHS-depleted by treatment with BSO. The analysis of all results allowed us to distinguish between the increase in GSH intracellular levels due to intact GSH uptake by specific transporters, and that due to GSH degradation by gamma-GT activity and subsequent absorption of degradation products with intracellular resynthesis of GSH; both these mechanisms seemed to be involved in increasing GSH content in heart after oral GSH administration. Jejunum, lung and brain took up GSH mostly intact, by specific transport systems, while in liver GSH uptake occurred only by its breakdown by gamma-GT activity followed by intracellular resynthesis.