An investigation on the health effects of occupational exposure to motor vehicle exhaust and environmental pollutants was carried out on traffic wardens in Milan (Italy). Randomized samples of 292 traffic wardens (exposed group) and 60 hospital staff members (control group) underwent a physical examination and laboratory tests. No significant difference was observed between the exposed and control groups as regards general morbidity, apart from musculo-skeletal disorders in females. The mean blood lead level (PbB) among traffic wardens was 15.2 micrograms/dl compared with 11.7 in control (p less than 0.01). The carboxyhaemoglobin concentration (COHb) in traffic wardens at the beginning of the shift was 2.8% for smokers and 1.2% for non-smokers (3.0% and 0.9% respectively in controls). At the end of the shift COHb in the exposed group was 4.3% for smokers and 2.5% for non-smokers (p less than 0.01). PbB was significantly correlated (r = 0.17) with Median Nerve Motor Conduction Velocity (NCV) in the exposed but not in the control group. The same pattern was observed for the correlation of PbB and Systolic Blood Pressure (SBP) (r = -0.24). COHb was significantly correlated with HDL cholesterol (r = -0.20) in the exposed group only. It is questionable whether very low PbB levels can affect NCV and SBP directly or rather whether PbB, as well as COHb, should be regarded as tracers of exposure to those urban pollutants leading also to cardiovascular and nervous disorders.