Survival of human bronchial epithelial cells after administration of four chemical carcinogens was measured in a donal assay. Human bronchial epithelial cells were obtained from outgrowths of explanted tissue pieces. Serum-free medium was used for both explant culture and donal growth. The donal assay could be performed on three substrata: plastic dishes alone, protein-coated dishes, and inactivated Swiss 3T3 cells. Several other cell lines supported donal growth of the human cells. Fetal bovine serum was inhibitory to colony formation on plastic and protein-coated dishes, but had no effect on the growth of bronchial cells on 3T3 feeder cells. Little variation among individuals in cytotoxicity of N-methyl-N'-nitro-N-nitrosoguanidine (MNNG) and K2CrO4, a possible human lung carcinogen, was observed, but in the case of benzo[a]pyrene (BP) and 7,12-dimethylbenz[a]anthracene (DMBA), large variations in survival were found between cultures derived from different individuals.