The report presents risk assessment-related aspects of a multidisciplinary study of indoor coal smoke pollution and lung cancer in Xuan Wei County, Yunnan Province, China. Xuan Wei presents a unique natural experiment in environmental carcinogenesis because lung cancer mortality rates and indoor pollution exposures vary widely within the County. Current evidence links lung cancer with domestic burning of 'smoky coal,' as opposed to 'smokeless coal' and wood. Efforts to determine the most carcinogenic components of smoky coal pollution are in progress, as are efforts to develop a quantitative relationship of pollution dose with lung cancer response in Xuan Wei. Some available evidence suggests that the composition of indoor pollution does not vary greatly throughout Xuan Wei, and thus that lung cancer risk is a function of overall pollution exposure. Other evidence suggests that different Xuan Wei fuels exhibit different carcinogenic potencies. On-site and laboratory studies are being conducted to distinguish between these possibilities.