In a case-control study 192 patients with histologically confirmed prostate cancer were compared with 210 men in whom carcinoma of the prostate had been histologically excluded. Cases and controls were recruited from two urological practices in Hamburg and Frankfurt/M. and from the urologic policlinic at the University of Frankfurt/M. The probands were questioned about smoking habits and alcohol consumption, about all occupational activities of least one years' duration, and about exposure to specific substances. Odds ratios (OR) were calculated using logistic regression analysis, adjusting for age, region and smoking. There were no differences between patients and controls in self-reported occupational exposures or the consumption of alcohol or smoking. There was a positive association between having worked in transportation/communication and having prostate cancer (p for trend = 0.006): ORs varied according to the number of years worked as follows: 1-10 years versus never; OR = 0.6 (95% CI: 0.3-1.2), 11-30 years, OR = 2.0 (95% CI: 0.8-4.8), > 30 years OR = 3.2 (95% CI: 1.3-7.5). Work in other occupational groups was not associated with an increased risk for prostate cancer. These results suggest that transport work may be associated with the development of prostate cancer.