The study of Xuan Wei fuel use and lung cancer mortality and also the interim case-control study suggested an association between domestic smoky coal use and Xuan Wei lung cancer. The collaborative studies of physical characterization, chemical analysis, and toxicology further substantiated this linkage. The Xuan Wei residents who used smoky coal inhaled extremely high concentrations of most submicron-sized particles, which were composed mostly of organic compounds (72%), including mutagenic and carcinogenic organic compounds (especially in the aromatic and polar fractions). In comparison to wood and smokeless coal combustion emissions, the organic extracts of smoky coal emission particles showed a much higher activity of genotoxicity and carcinogenicity. The results all point to a strong etiological link between the complex organic mixtures from smoky coal emissions and Xuan Wei lung cancer.