Hepatic levels of S-adenosylmethionine (AdoMet), glutathione and the microsomal enzymes p-nitroanisole demethylase and benzo(a)pyrene hydroxylase were measured in male and female rats fed a diet marginally deficient in choline and methionine and void of folic acid (lipotrope deficient) or an adequate diet for 0-14 wk with and without added 2-acetylaminofluorene (AAF). The urinary metabolites of AAF were determined throughout the experimental period. After 2-4 wk of dietary administration, hepatic AdoMet levels were 43% lower in male rats fed the lipotrope deficient diet than in male rats fed the lipotrope adequate diet. No differences were found in hepatic AdoMet of females fed the lipotrope deficient or lipotrope adequate diets for 2-14 wk. Administration of AAF to lipotrope deficient female rats for 2 wk led to a transient decrease in hepatic levels of AdoMet. Administration of AAF for 2-14 wk did not significantly affect hepatic AdoMet in female rats fed the lipotrope adequate diet or in male rats fed either diet. Female rats fed the lipotrope deficient diet and treated with AAF excreted decreased proportions of N-hydroxy-AAF and increased proportions of 5-hydroxy-AAF in their urine. The urine of lipotrope deficient male rats treated with AAF contained increased proportions of N-hydroxy-AAF and decreased levels of 5-hydroxy-AAF. The urinary excretion of 7-hydroxy-AAF by male and female lipotrope deficient rats treated with AAF was similar to that in lipotrope adequate rats. The lipotrope deficient diet did not appear to alter the hepatic levels of glutathione. p-Nitroanisole demethylase or benzo(a)pyrene hydroxylase in male or female rats. Benzo(a)pyrene hydroxylase activity was lower in the livers of lipotrope deficient male rats treated with AAF for 8-14 wk than in the livers of lipotrope deficient rats not receiving the carcinogen. The altered metabolism of AAF correlated well with the previously reported effects of a marginal lipotrope deficiency on AAF [liver] carcinogenesis.