Butadiene is a suspect human carcinogen to which most people are exposed daily. Exposures are difficult to measure by air sampling. This study examines the relationship between air levels and several biomarkers of exposure. Biomarkers are substances analyzed in human tissues or waste products. Adducts are materials formed when a chemical reacts with a biological material. In this study we are looking at biomarkers in the blood: hemoglobin and DNA adducts, and urinary metabolites. If a strong relationship is found then the amounts of biomarkers in a person's blood or urine can tell us how much they have been exposed. The tests are being conducted on petrochemical workers who have a wide range of exposures to butadiene. An international group of investigators is conducting the study.