Workers are exposed to butadiene, isoprene and chloroprene in the manufacture of these monomers and in their use in the production of various elastomers. These include styrene butadiene rubber, polybutadiene, polyisoprene, butyl rubber and neoprene. Monomer production and extraction are done in typical closed chemical process units where low background levels of the monomers are the result of minor leaks in valves and pumps. Occasionally, higher levels occur as a result of planned or unplanned events that cause releases. Polymer production is also a closed process, but the occasional clogging of pipes and equipment with polymer requiring maintenance operations where some release is likely occurs much more often than for monomer production. For this reason, exposure levels are generally higher on polymer production units. Polymer finishing is essentially an open process, but almost all monomer should have been stripped from the polymer before finishing. Where small amounts of solvents or monomers remain in the polymer and are volatilized in finishing, they are captured by vapor control systems. As a result, exposures in finishing are typically low. Measured levels of exposure in recent years are presented. In general, modern levels of exposure are well below OSHA, ACGIH and other applicable limits. Few measurements were made prior to the 1970s, but epidemiological estimates made by modeling suggest that levels could have been quite high in the 1940s and 1950s. In these years, manual reactor cleaning was common, and pumps often leaked.