The interaction of the effect of dietary methionine (met) deficiency on the maintenance of hepatic glutathione (GSH) concentrations and the effect of chronic ethanol (EtOH) ingestion on the activity of the hepatic microsomal oxidation system were studied in relation to acetaminophen (ACAP) metabolism in mice. In the first study, adult, male mice were fed a diet that provided approximately one-half of the met requirement for 4 weeks and given a 15% EtOH solution as the sole source of drinking water in a 2 x 2 factorial design. The extent of ACAP-induced hepatotoxicity was greater in the met deficient mice, as shown by a reduced median lethal time following a lethal dose of ACAP and an increase in plasma glutamic-oxaloacetic transaminase (PGOT) activity following a sublethal dose. A more marked increase in PGOT activity was seen as a result of the interaction of met deficiency and EtOH consumption. Initial GSH levels were decreased and depletion following ACAP injection was greater in the met deficient groups. In the second study, mice were pair-fed an EtOH-containing liquid diet for 4 weeks that provided 46 or 100% of the met requirement in a 2 x 2 factorial design. There was an increase in hepatic microsomal protein content, relative liver weight, and hepatic microsomal aniline hydroxylase activity in the EtOH-fed groups indicating induction of microsomal oxidation by EtOH. Serum inorganic sulfate, hepatic free met, and GSH concentrations were decreased following a 300 mg/kg BW i.p. dose of ACAP. As in the first study, GSH depletion was greater in the met-deficient mice. The difference between the extent of ('35)S-met and ('14)C-methyl-met incorporation into hepatic proteins did not reflect differences in the hepatic transsulfuration pathway activity due to met deficiency. HPLC analysis of urinary ACAP conjugates showed a decrease in the amount of ACAP-sulfate conjugate excreted in the met deficient mice and an increase in excretion of ACAP sulfate and mercapturic acid derivatives by the EtOH-fed mice. These findings indicate that met deficiency compromises ACAP disposition in the mouse resulting in greater ACAP-induced hepatotoxicity and that chronic EtOH consumption may potentiate this effect by causing an increase in the formation of activated ACAP.