On April 27-28, 1995, the National Urban Air Toxics Research Center hosted a Symposium on Air Toxics: Biomarkers in Environmental Applications. The purpose of the symposium was to define the current state of the art in the application of biomarkers for environmental exposures to benzene, toluene, styrene, 1,3-butadiene, polycyclic aromatic hydrocarbons, manganese, and chromium. Sensitive, specific, and cost-effective biomarkers of exposure, effect, and susceptibility may greatly improve our knowledge of the human health impacts of air toxics exposures. Presentations were made on the first day that provided state-of-the-art background for the need, use, and ethical considerations in biomarker research and applications. In workshops held during the symposium, a number of recommendations were made regarding the use and need for additional research with biomarkers. In general, the sensitivity and specificity of biomarkers for environmental exposures, need to be improved. Reliable effect and susceptibility biomarkers are not available for these compounds. More research needs to be done to establish and evaluate biomarkers, linked to health effects through mechanistic studies, at environmentally relevant exposure levels.