An industrial hygiene survey and an epidemiological study were performed to estimate diesel exhaust exposure levels of workers in the trucking industry. The relation to lung cancer was assessed. The study included 996 individuals with lung cancer and 1085 comparisons who died between 1982 and 1983 and had 20 or more years tenure in the Teamsters Union. Nonexposed subjects included workers employed in Teamster jobs but not exposed to diesel exhaust. Exposed individuals included road drivers, local drivers, mechanics, and dock workers. Elemental carbon analysis was performed as a marker for diesel exhaust exposure. Mechanics had the highest elemental carbon exposure in the industrial hygiene survey, followed by road drivers, local drivers, and dock workers. Road drivers showed increased risk with duration of employment. Compared to nonexposed subjects, individuals with the highest levels of diesel exhaust exposure exhibited an excess lung cancer risk of about 50%. The authors conclude that increased lung cancer risk for mechanics, drivers, and other trucking industry personnel may be related to diesel exhaust exposure.