UDS activity in the rat liver of the human carcinogens benzidine and 4-aminobiphenyl, and the rodent carcinogens 3,3'-dichlorobenzidine and direct black 38.

The activity of benzidine and three structurally related carcinogens in an in vivo/in vitro rat liver assay for unscheduled DNA synthesis is described. The first three of these chemicals, benzidine, 4-aminobiphenyl (4AB) and Direct Black 38 have been reported as positive in this assay by other investigators, albeit the data reported for 4AB were limited. The fourth compound, 3,3'-dichlorobenzidine has not been studied in this assay before. Each compound gave a clear positive response under conditions of routine testing.