Experiments were conducted to examine the role of zinc in the prevention of bromobenzene hepatoxicity in male rats. Bromobenzene (BB) (7.5 mmol/kg, ip) produced a marked hepatotoxicity as evidenced by increases in plasma alanine aminotransferase (ALT) and aspartate aminotransferse (AST) activities and a marked depression in hepatic glutathione (GSH) content 24 hr after administration. The administration of zinc (92 μmol Zn/kg, ip, at 48 and 24 hr prior to the bromobenzene) ameliorated the bromobenzene elevations in plasma AST (25%) and plasma ALT (50%) but did not alter the decreases in hepatic GSH. Following administration of [¹⁴C]BB, the radioactive label was distributed primarily in the cytosolic and lipid fractions derived from liver homogenates. Furthermore, the subcellular distribution of [¹⁴C]BB was not altered by zinc pretreatment. The extent of covalent binding of [¹⁴C]BB metabolites to hepatic tissue was significantly depressed in zinc-treated rats. Zinc induced the hepatic levels of metallothionein but [¹⁴C]BB did not bind to this sulfhydryl rich protein. Further experiments showed that zinc treatment depressed cytochrome P-450 content, the activity of NADPH cytochrome c reductase, and the metabolism of aniline, but not that of ethylmorphine. These studies suggest that the hepatoprotective effect of zinc against bromobenzene toxicity does not involve altered binding of the reactive toxic metabolite to glutathione or metallothionein, but it may be mediated by the inhibitory effect of zinc on the microsomal cytochrome P-450-dependent drug metabolizing system.