The effect of dietary cabbage (Brassica oleracea) on the binding of aflatoxin B1 (AFB1) to hepatic DNA and on the activities of liver and intestinal microsomal and cytosolic enzymes was studied in weanling male Fischer 344 rats. Freeze-dried cabbage was fed to rats at a level of 25% in the diet for 21 days, while others received a basal diet. In the cabbage-fed group there was an 87% (P less than 0.01) reduction in the binding of AFB1 to hepatic DNA 2 hr after the ip injection of [3H]AFB1 (3 micrograms/kg). There was also a 41% (P less than 0.05) increase in liver weight expressed relative to body weight. Hepatic and intestinal glutathione S-transferase activities were significantly increased (2.1- and 2.3-fold, respectively) over those in rats fed the basal diet. Hepatic and intestinal microsomal epoxide hydrolase activities were significantly increased (2.6- and 1.4-fold, respectively) over the basal group. Intestinal aryl hydrocarbon hydroxylase (AHH) and ethoxycoumarin O-deethylase (ECD) activities were significantly increased (2.3- and 2.5-fold, respectively), over the basal group but dietary cabbage had no significant effect on hepatic AHH or ECD activities.