This questionnaire-based study found a significantly higher prevalence of chronic bronchitis, asthma, and several other symptoms in 116 Copenhagen street cleaners who were exposed to traffic-related air pollution at levels that were slightly lower than the 1987 World Health Organization-recommended threshold values, compared with 115 Copenhagen cemetery workers exposed to lower pollution levels. Logistic regression analysis, controlling for age and smoking, was conducted, and odds ratios and 95% confidence intervals were calculated to be 2.5 for chronic bronchitis (95% confidence interval = 1.2-5.1), 2.3 for asthma (95% confidence interval = 1.0-5.1), and 1.8-7.9 for other symptoms (95% confidence interval = 1.0-28.2). Except for exposure to air pollution, the two groups were comparable, i.e., they had similar terms of employment and working conditions. The exposure ranges during an 8-h work day, averaged from readings taken at five monitored street positions, were: 41-257 ppb nitric oxide (1-h max: 865 ppb); 23-43 ppb nitrogen dioxide (1-h max: 208 ppb); 1.0-4.3 ppm carbon monoxide (8-h max: 7.1 ppm); 14-28 ppb sulfur dioxide (1-h max: 112 ppb); and 10-38 ppb ozone (1-h max: 72 ppb).