Serum glutamyl transferase (gamma-GT), serum total protein, albumin, aspartate aminotransferase (GOT), alanine aminotransferase (GPT), alkaline phosphatase and bilirubin were measured in 55 males and 45 females suffering from O. viverrini infection and in apparently healthy non-infected individuals. A decrease in total protein, albumin and bilirubin, as well as an increase in GOT, GPT and gamma-GT was observed in males with O. viverrini infection, whereas alkaline phosphatase remained unaffected. In female patients with O. viverrini, serum total protein and albumin also decreased, GOT and GPT increased, whereas gamma-GT remained unchanged. The difference in gamma-GT alteration between females and males is discussed with regard to the possible significance of alcohol consumption and in relation to the parasitic infection and its possible implications for malignancy, associated with liver fluke infection.