Abelson's editorial contains an unbalanced and cursory review of 1,3-butadiene toxicity and of the recent National Institute for Occupational Safety and Health (NIOSH) risk assessment of butadiene. A thorough review of the metabolic, toxicologic, and epidemiologic data for butadiene is available. The NIOSH risk assessment was based on a recent National Toxicology Program study, in which B6C3F1 mice were exposed to butadiene concentrations of 6.25 to 625 parts per million (ppm), a range which overlaps that of actual occupational exposures. In order to evaluate the sensitivity of our risk estimates to modeling assumptions we applied time-to-tumor models under several asssumptions. None of these models led to the 100% predicted response at 2 ppm that was implied in the editorial.