The relationship between truck driving and bladder cancer mortality was investigated in a case-control study in New Hampshire and Vermont. In-person interviews were conducted with the next-of-kin of 325 bladder cancer cases and 673 controls who died during 1975-79. There were 35 cases and 53 controls who had ever been employed as truck drivers [odds ratio (OR)=1.5, 95% confidence interval (CI)=0.9, 2.6]. There was a statistically significant, but inconsistent, positive association between number of years of truck driving and the OR's, rising to 2.3 (1.2,4.1) for 5 years or more of truck driving. Risk was greatest in men who began driving in the 1930's and 1940's (OR=2.6, 95% CI=1.3,5.1) and among residents of two of the most urbanized counties (OR=3.0, 95% CI=1.2,7.4). The association of bladder cancer with truck driving was unaffected by control for possible confounding factors, such as cigarette smoking and coffee drinking. It was not possible to determine whether the risks associated with truck driving were specifically due to diesel fumes. Truck drivers reporting diesel exposures had an OR=1.8 (95% CI=0.5,7.0), but those without diesel exposure still had an OR=1.5 (95% CI=0.8,2.7). Twenty-six cases and 39 controls reported exposure to diesel emissions in any occupation (OR=1.5, 95% CI=0.8,2.8), and a significant duration-response relationship was seen, rising to threefold for those employed in such jobs for 30-39 years.