The relationship between occupation and cancer of the lower urinary tract in Detroit was examined by means of a population-based case-control study conducted as part of the National Bladder Cancer Study. Three hundred three white male patients with transitional or squamous cell carcinoma of the lower urinary tract and 296 white male controls selected from the general population of the study area were interviewed to obtain lifetime occupational histories. Our findings suggested that truck drivers have a significant increased risk of lower urinary tract cancer [relative risk = 2.1; 95% confidence interval (Cl) = 1.4-4.4]. A significant trend in risk was apparent with increasing duration of employment as a truck driver (P = 0.004); the relative risk estimated for truck drivers employed at least 10 years was 5.5 (Cl = 1.8-17.3). Truck drivers with a history of operating vehicles with diesel engines experienced a significant elevated risk compared to non-truck drivers (relative risk = 11.9; Cl = 2.3-61.1), but whether the increased risk observed among truck drivers was attributable to diesel exposure could not be evaluated. Nonsignificant excess risks were also seen for tool and die makers as well as for workers in several other industries and occupations. Employment in the motor vehicle manufacturing industry was associated with no significant excess risk of lower urinary tract cancer (relative risk = 1.1; Cl = 0.8-1.5).