Fischer 344 rats were fed a low-fat high carbohydrate (HC) diet, an isocaloric fat-containing (IC) diet, a hypercaloric fat-containing (HF) diet or a commercial rodent chow. The effects of these diets were studied on the binding of aflatoxin B (AFB1) to exogenous DNA, and on the activities of hepatic glutathione transferases (GSTs), cytochromes 2B1 and 1A1. Microsome-mediated binding of [3H]AFB1 to exogenous DNA was significantly lower in the HC-rats than in the chow and IC-fed rats. No significant differences were noted between HF and either HC or IC rats. There was no significant difference in hepatic GST activity of rats fed the different diets. Our results suggest that high-carbohydrate low-fat diets reduce microsome mediated epoxidation of AFB1 to a larger extent than high-fat diets. In general, high fat diets increased cytochrome 1A1 and 2B1 activities relative to chow and high carbohydrate diet. This suggests greater detoxification of AFB1, thus reducing the amount of AFB1 available for hepatic macromolecular binding.