Short term in vivo studies were performed to study biological effects of the common air pollutants SO2 or NOx and their influence on the genotoxic activities of nitrosamines. Hepatocytes and lung cells were isolated from Sprague-Dawley rats which had inhaled 50 p.p.m. of SO2 or NOx for 2 weeks. After incubating the cells for 1 h, genotoxicity was determined in hepatocytes by measuring DNA single-strand breaks induced by N-nitroso-acetoxymethylmethylamine, N-nitrosodimethylamine and N-nitrosomethylbenzylamine. Parameters of toxicity (trypan blue exclusion and leakage of serum enzymes) were determined in both liver and lung cells also following 1 h incubation. The activities of aryl hydrocarbon hydroxylase (AHH), nitrosodimethylamine demethylase (NDMA-D) and glutathione-S-transferase (GST) were determined in subcellular microsomal fractions isolated from lung and liver tissues. Finally, as a measure of overall toxicity, the activities of various serum enzymes were determined in the blood serum of the rats. It was found that the induction of DNA single-strand breaks by three nitrosamines was decreased in hepatocytes from SO2-treated animals. The viability of rat hepatocytes and of rat lung cells, as determined by trypan blue exclusion, was similar in all three treatment groups immediately after isolation, as well as after 1 h incubation with DMSO or with the nitrosamines. In contrast, the leakage of enzymes was different in hepatocytes of SO2-treated rats, since lactate dehydrogenase activity was decreased. Leakage of enzymes from the lung cells did not differ from group to group, but was lower than from hepatocytes. Foreign compound metabolizing enzymes were mainly decreased in NOx-treated animals, namely AHH, NDMA-D and GST in liver and GST in the lung. For SO2-treated animals NDMA-D was increased in liver and GST was decreased in lung. Blood serum enzyme levels were not greatly different from each other, except for lactate dehydrogenase which was elevated in SO2-exposed animals.