The effects of vegetables on the activities of various metabolizing enzymes in liver and intestine have been studied intensively, whereas studies on effects on testicular metabolizing enzymes are lacking. The present report is the first describing the effects of dietary broccoli on the activities of a number of xenobiotic metabolizing enzymes from rat testes. Groups of male Wistar rats were fed a semisynthetic diet with 10% (w/w) freeze-dried broccoli for 1 week. Different broccoli samples with varying content of glucosinolates were used. Dietary broccoli significantly increased the activities of two testicular phase II enzymes--glutathione S-transferase (1.6-fold) and UDP-glucuronosyl transferase (1.8-fold). The activities of these enzymes differed significantly depending on the conditions during cultivation of the broccoli, because of differences in the content of glucosinolates and other secondary plant metabolites. The levels of two glutathione S-transferase subunits, rGSTM2 and rGSTA, were determined using Western blotting analysis and the levels of both subunits were reduced in animals fed broccoli grown at low S-fertilizer level. Broccoli did not statistically significantly modulate the activities of the phase I enzymes, epoxide hydrolase or NAD(P)H quinone-oxidoreductase, or the phase II enzyme p-sulphotransferase, or the anti-oxidative enzymes catalase and total glutathione peroxidase in rat testes. In general, dietary broccoli affects phase I and phase II enzyme levels in rat testes much less than found in liver, however, two rat testicular phase II xenobiotic metabolizing enzymes were induced.