The effect of type (corn oil or lard) and quantity (5 or 20%) of dietary fat and 1,2-dimethylhydrazine (DMH) on the composition of biliary bile acids, fecal bile acids, and neutral sterols was studied in rats exposed to a given regimen for two generations prior to s.c. treatment with DMH for 20 weeks. Biliary excretion of total bile acids as well as cholic acid, beta-muricholic acid, ursodeoxycholic acid, and deoxycholic acid was higher in rats fed a diet containing 20% corn oil or lard than it was in rats fed diets containing 5% corn oil or lard. Treatment of animals with DMH produced an increase in biliary total bile acids, cholic acid, hyodeoxycholic acid, and deoxycholic acid irrespective of diets. High-fat (corn oil or lard at 20% level) intake was associated with an increased excretion of fecal neutral sterols and bile acids. The excretion of deoxycholic acid, lithocholic acid, and 12-ketolithocholic acid was increased in rats fed high-fat diets. The source of fat had no major influence on the excretory pattern of cholesterol metabolites and bile acids. DMH-treated animals excreted higher levels of fecal coprostanol, coprostanone, deoxycholic acid, lithocholic acid, and 12-ketolithocholic acid than did controls.