Different parameters of biological monitoring were applied to 26 benzene-exposed car mechanics. Twenty car mechanics worked in a work environment with probably high benzene exposures (exposed workers); six car mechanics primarily involved in work organization were classified as non-exposed The maximum air benzene concentration at the work places of exposed mechanics was 13 mg/m 3 (mean 2 6 mg/m 3 ) Elevated benzene exposure was associated with job tasks involving work on fuel injections, petrol tanks, cylinder blocks, gasoline pipes, fuel filters, fuel pumps and valves The mean blood benzene level in the exposed workers was 3 3 jig/l (range 0 7-13 6 g/l) Phenol proved to be an inadequate monitoring parameter within the exposure ranges investigated The muconic and S-phenylmercapturic acid concentrations in urine showed a marked increase during the work shift Both also showed significant correlations with benzene concentrations in air or in blood The best correlations between the benzene air level and the mercapturic and muconic acid concentrations in urine were found at the end of the work shift (phenylmercapturic acid concentration: r = 0 81, P < 0 0001 ; muconic acid concentration: r = 0 54, P < 0 05) In conclusion, the concentrations of benzene in blood and mercapturic and muconic acid in urine proved to be good parameters for monitoring benzene exposure at the workplace even at benzene air levels below the current exposure limits Today working as a car mechanic seems to be one of the occupations typically associated with benzene exposure.