Abstract: Aims: Occupational/environmental exposure to hepatotoxins has recently been implicated in nonalcoholic steatohepatitis (NASH). The aims of this study were to determine the presence and frequency of NASH in a large group of workers chronically exposed to several volatile petrochemical products in an industrial area in north-east Brazil and to observe its course in workers removed from the work environment. Methods: 1500 asymptomatic workers were screened with standard liver blood tests during 1994–5. Those with elevated transaminases (>3× normal) on 3 occasions were evaluated further both clinically and with serum HBsAg, anti-HCV, ferritin, lipids and autoantibody determination. Patients with either no etiological diagnosis, positive HBsAg/anti-HCV serology and/or excess alcohol intake underwent liver biopsy. Those with obesity, diabetes or an isolated abnormal GGT were excluded. Of workers diagnosed as having NASH (compatible histology and no excess alcohol intake), a proportion were removed from the work environment and evaluated monthly with liver blood tests and a repeat liver biopsy 8–14 months later. Results: 112 workers had abnormal transaminases and 32 fulfilled the criteria for liver biopsy. 20 of these were classified as NASH, the remainder had viral hepatitis (n=6), alcoholic liver disease (n=5) or portal vein thrombosis (n=1). In all of the 10/20 who were removed from the work environment, their aminotransferases and GGT gradually decreased and their histology improved. Conclusions: These results demonstrate that NASH can occur following chronic exposure to volatile petrochemical substances in the workplace. Exposed workers should be regularly screened for the presence of liver damage and ideally removed from the work environment where possible.