Groups of Alderly Park male rats were dosed concomitantly with 2-AAF by gavage at doses between 0.01 mg/kg and 40 mg/kg, and livers sampled 2-72h later. The liver of one group of animals was perfused to yield hepatocytes which were assayed in vitro for unscheduled DNA synthesis (UDS) via incorporation of tritiated thymidine and autoradiography. DNA was extracted from the livers of the other group and DNA adduct levels determined using the (32)P-postlabelling technique. The major C-8 2-aminofluorene/guanosine and three minor adducts were quantitated enabling the relative sensitivity of the two techniques to be compared. A dose and time related UDS response was observed, which at the most sensitive time point enabled DNA repair to be discerned at a dose level of 0.1 mg/kg of 2AAF, a response classified formally at 5 mg/kg 2AAF. Only the C-8 adduct as determined by (32)p-postlabeling analysis was discernible at doses as low as 0.01 mg/kg of 2AAF. It is concluded that as part of a well-defined dose response, UDS can be discerned with confidence for doses of 2AAF between 0.1-5 mg/kg and DNA adducts for doses of 2AAF between 0.01-1.0 mg/kg. (Copyright (c) 1991 Elsevier Science Publishers B.V.)