The effects of intracerebroventricularly (i.c.v.) administered gamma-glutamylcysteine (gamma-GC) and glutathione (GSH) monoethyl ester, subcutaneously (s.c.) injected L-2-oxo-4-thiazolidinecarboxylic acid (OTC) and intraperitoneally (i.p.) administered cysteine on the concentration of GSH in rat brain were investigated. The brain content of GSH, cysteine and gamma-GC was determined by HPLC with electrochemical detection (gold/mercury electrode) using N-acetylcysteine as internal standard. A dose-dependent increase in the GSH concentration (145-170% of controls) was found in the substantia nigra (SN) and in the rest of the brain stem after injection of gamma-GC, whereas no significant alterations in GSH were observed in the striatum and in the cerebral cortex. High levels of gamma-GC could be detected in the brain tissue after the administration, and the concentration of cysteine did also increase markedly after gamma-GC injection in all brain regions assessed. I.c.v. administration of L-buthionine sulfoximine (L-BSO) reduced the brain concentration of GSH by 50-70% within 24 hr. Injection of gamma-GC 24 hr after L-BSO resulted in an increase in GSH up to control values within 1-3 hr in the SN and the rest of the brain stem, whereas only a slight increase in GSH was observed in the striatum and the cerebral cortex. The concentration of GSH in the striatum and SN did not change after i.p. injection of cysteine, but a slight increase in the GSH concentration in the limbic region was observed. GSH monoethyl ester (i.c.v.) and OTC (s.c.) did not produce any significant increase in the GSH concentration in the brain. When the GSH concentration had been reduced by administration of L-BSO (i.c.v.; 24 hr) subsequent injection of GSH monoethyl ester led to a slight increase in the striatal and limbic GSH levels. These data show that, of the drugs studied, gamma-GC was the most effective in increasing brain GSH. It could thus serve as a valuable tool in future studies regarding metabolism and function of GSH in the brain. The observed difference in the effects of gamma-GC in different brain regions indicate that the brain tissue is not homogeneous with regard to GSH synthesizing capacity.