Epidemiological and experimental studies have demonstrated that lead and cadmium are responsible for renal dysfunction. Urinary trehalase is known as a good marker of proximal tubular renal brush border destruction in the population environmentally exposed to cadmium. The aim of this study was to determine the impact of occupational exposure to lead on the renal function and urinary trehalase activity. The study was carried out in 68 workers, aged 46 +/- 6 years, employed in a copper foundry. Blood lead, cadmium, copper and manganese concentrations were measured by atomic absorption spectrophotometry. Urinary trehalase activity was determined by the method of Nakano and Itoh. Trehalase activity was increased in copper smelters as compared to controls. There also was a positive linear correlation between blood lead level and urinary trehalase activity (r = 0.44; p < 0.05). Negative correlations between blood lead and copper concentrations (r = -0.30; p < 0.05) and between serum copper and trehalase level (r = 0.68; p < 0.001) were found. The results show that urinary trehalase activity could be a good indicator of the renal brush border dysfunction in copper smelters. This marker could be useful in the early diagnosis of nephrotoxic effect of lead.