Researchers from the National Institute for Occupational Safety and Health (NIOSH) of the Centers for Disease Control and Prevention conducted an extent-of-exposure study of 1,3-butadiene monomer, polymer and end-user industries to assess occupational exposure to butadiene and to evaluate control technologies. The findings of the exposure assessment are reported here. Walk-through surveys were conducted in 11 monomer, 17 polymer and two end-user plants; in-depth industrial hygiene surveys were conducted at four monomer, five polymer and two end-user plants. Airborne exposure concentrations of butadiene were determined for various job categories by personal sampling. The samples were analysed by a new method developed at NIOSH that is sensitive to 0.2 microgram per sample. A total of 687 personal (full-shift and short-term) and 232 area samples were taken. The results indicate that all exposures were well below the current permissible exposure limit of the US Occupational Safety and Health Administration of 1000 ppm. The US Occupational Safety and Health Administration (1990) has proposed a new standard that would reduce exposure to 2 ppm. Exposures ranged from less than 0.005 ppm to 374 ppm, and 3.7% of the samples contained more than 10 ppm, 7.8% more than 2 ppm but less than 10 ppm and 88.5% less than 2 ppm. We recommend means for reducing exposure by the use of engineering controls.