(1) a history of at least 1
year occupational exposure to unleaded petrol; and (2) lack of history of exposure to other known nephrotoxic and hepatotoxic agents and no job history of exposure to other chemical materials. A reference group was composed of healthy individuals without current or past exposure to agents known to cause any hepatotoxic or nephrotoxic response. Collectively, 400 individuals (200 reference individuals and 200 exposed workers) entered the study. Exposed participants were the employees of all (20 active) private petrol stations in Shiraz.