The metabolic activation of several chemical classes of procarcinogens is being studied in cultured human bronchi. Previous studies have shown that carcinogenic polynuclear aromatic hydrocarbons are metabolically activated by the bronchial epithelium. In the study reported here, dimethylnitrosamine and 1,2-dimethylhydrazine were also found to bind to both cellular DNA and protein. Bronchial DMA was methylated in both the O-6 and N-7 positions of guanine. In addition to polynuclear aromatic hydrocarbons, an aliphatic nitrosamine and a methylhydrazine can now be added to the list of xenobiotic chemical carcinogens metabolized by human bronchus.