Human exposure to complex mixtures of genotoxic indoor air pollutants can be assessed using several different bioanalytical methods. External exposure can be assessed using micromutagenesis methods to measure human exposure to mutagens. Internal exposure and dose can be assessed using macromolecular adducts (e.g., DNA adducts). Urinary metabolites of specific components and the mutagenicity of urine have also been used as bioindicators of exposure. External exposure to the mutagenic activity of tobacco smoke is readily measured indoors and results in the highest reported exposure to mutagens. External exposure to mutagens from ETS has been compared to internal exposure by using urinary measurements of the nicotine metabolite, cotinine. The organic matter (tar) from particles emitted from tobacco smoke and other combustion sources is genotoxic to cells, carcinogenic to animals, and results in the formation of DNA adducts.