Tobacco smoking causes millions of cancer deaths annually. Tobacco smoke is a complex mixture of thousands of chemicals including many known animal carcinogens. Because many carcinogens from DNA adducts in target animal or human tissues, the detection of the formation of adducts using such methods as postlabeling, immunoassay, fluorescence spectroscopy, and mass spectrometry is a means of monitoring human exposure to tobacco carcinogens. Smokers are at increased risk of cancer in many organs, and studies have revealed either specific adducts related to smoking or increased levels of adducts in the lung, bronchus, larynx, bladder, cervix, and oral mucosa of smokers. In a limited number of studies, the adducts and the carcinogens responsible for them have been identified. Some studies have demonstrated higher levels of adducts in the white blood cells of smokers, while other studies indicate other sources of genotoxic agents, including diet, can contribute to the DNA damage observed in these cells.