The protective effect of S-adenosyl-L-methionine (SAMe) on bromobenzene (BB)- or D-galactosamine (GalN)-induced damage to isolated rat hepatocytes and its effect on cellular glutathione (GSH) levels were investigated. SAMe at concentrations of 0.5 to 3.0 mmol/L significantly reduced lactate dehydrogenase leakage from cells exposed to 1.6 mmol/L BB (P < .05 to .001) during 2 hours' incubation. GalN at 25 to 50 mmol/L induced a marked increase of LDH leakage from the cells during the later stage of 24 hours' incubation and SAMe at 1.0 mmol/L clearly attenuated the LDH leakage in GalN (25 mmol/L)-exposed cells. The GSH content in the cells exposed to 2.4 mmol/L BB for 150 minutes was markedly decreased, and further decreased during 24 hours' incubation. SAMe (1.5 mmol/L) both reduced LDH leakage and corrected GSH depletion in cells exposed to 2.4 mmol/L BB. The GSH content in 25 and 50 mmol/L GalN-exposed cells was strikingly diminished to 51.2% and 32.8% of the controls, respectively, during 24 hours' of exposure. SAMe at 1.5 mmol/L significantly reduced the loss in GSH content in 25 mmol/L GalN-exposed cells. The findings show that SAMe has beneficial effects on both BB- and GalN-induced toxicity to rat hepatocytes. The main mechanism behind the protective effect of SAMe on BB and GalN toxicity seems to be associated with enhancement of GSH synthesis in the cells.