The formation of hepatic DNA adducts in male Sprague-Dawley rats following i.p. administration of benzo[f]quinoline (BfQ) was examined using a 32P-post-labeling assay. BfQ exhibited a low binding (11-27 amol adducts/microgram DNA) to liver DNA. Two BfQ-nucleoside adducts (one major and one minor) were detected. The BfQ-DNA adducts formed in vivo were chromatographically distinct from the adducts formed by the reaction of calf thymus DNA in vitro with BfQ-5,6-oxide, syn-7 beta,8 alpha-dihydroxy-9 beta,10 beta-epoxy-7,8,9,10-tetrahydroBfQ, anti-9 alpha,10 beta-dihydroxy-7 alpha,8 alpha-epoxy-7,8,9,10-tetrahydroBfQ, or anti-7 beta,8 alpha-dihydroxy-9 alpha,10 alpha-epoxy-7,8,9,10-tetrahydroBfQ-N- oxide. These results suggest that the bay-region diol epoxide of BfQ, unlike the bay-region diol epoxide derivatives of polynuclear aromatic hydrocarbons, is not involved in the covalent binding of BfQ to DNA.