The production of rubber and rubber products is a large and diverse industry. Natural rubber, obtained from plantations in Africa and Asia, accounts for only about 25% of the rubber used in industry. Synthetic alternatives, developed during World War II, are the primary sources of raw materials today. Health hazards in synthetic rubber production are primary related to exposure to monomers. An excess incidence of leukemia has been observed in styrene/butadiene rubber production, attributed to exposure to 1,3-butadiene. Excesses of cancer and respiratory disease have been reported, although specific causative agents are rarely identified. Exposures have varied greatly over the years, based on changes in materials used, work practices, and ventilation. In modern industry, exposures to noise, skin and respiratory irritants, and ergonomic stressors remain important. The tire industry, in particular, has been studied extensively over the past 50 years.