The metabolism of [3H]-4-chlorobiphenyl (CB) by Chinese hamster ovary cell cultures resulted in the formation of lipophilic hydroxylated metabolites, trichloroacetic acid soluble conjugates and covalent macromolecular adducts. The major lipophilic metabolite was chromatographically similar to 4'-chloro-4-biphenylol. The intracellular macromolecules were fractionated into protein, RNA and DNA. Although protein was the major target of covalent interaction with [3H]-CB and contributes 85% of the macromolecular binding, the specific binding of [3H]-CB to DNA was 3.5 and 1.4 times higher than that observed for protein and RNA respectively. Incubation of the CHO cells with 10 mM CB, [3H]-thymidine and 10 mM hydroxyurea for 2.5 hr resulted in a 1.6 fold increase in unscheduled DNA synthesis. The data demonstrated that the readily metabolized CB congener not only reacts with mammalian cell macromolecules, including DNA, but the DNA damage can also be demonstrated by its subsequent repair.