In numerous epidemiologic studies, environmental and occupational substances such as sodium dichromate (Na2Cr2O7), benzo[a]pyren (B(a)P), and N'nitroso-diethanolamine (NDELA) have been shown to be of potential carcinogenic risk on human epithelial cells in the upper aerodigestive tract.Using the alkaline microgel electrophoresis technique (comet assay). mucosal cells isolated from biopsies of the upper aerodigestive tract (nose, paranasal sinuses, mouth, pharynx, larynx, and tonsils) were used to analyze target sites for different genotoxic substances and specific sensitivities of each donor. The cells were freshly isolated by enzymic digestion. 0.5-1 x 10(6) cells per donor were obtained with viabilities between 80-100%. After in vitro incubation, the cells were subsequently subjected to the single cell microgel electrophoresis assay. Results were evaluated regarding the personal history of each donor, focusing on previous exposure to tobacco, alcohol, and occupational compounds.Na2Cr2O7 induced strong genotoxic damage in the nasal and paranasal sinus epithelia as well as in mucosa cells of the larynx. NDELA caused significant damage in mouth cavity epithelia and showed also to be harmful towards mucosa of pharynx and larynx. B(a)P induced fewer DNA strand breaks in mucosal cells of mouth, pharynx and larynx. Significant differences between individuals were apparent for tissue samples from different donors. The genotoxic damage induced in cells of donors with a history of chronic alcohol consumption was significantly higher than in cells of patients without chronic abuse of alcohol.The data shows that DNA damage in human epithelial cells of the upper aerodigestive tract induced by environmental and occupational substances can be demonstrated using the microgel electrophoresis technique. The influence of chronic alcohol consumption on the genotoxic effects of substances such as NDELA and B(a)P showed the importance of evaluating preexisting compounding factors.