The prevalence of hepatitis G virus (HGV) infection in patients with liver diseases in Singapore and its pathogenic role in these patients was studied. One hundred and forty-eight patients who had chronic hepatitis or acute non A-E hepatitis were studied. Presence of HGV RNA was determined by nested polymerase chain reaction of the 5'non-coding region of the virus in all the patients. Hepatitis G IgG antibody to the envelope (E2) antigen was tested with an enzyme immunoassay (Boehringer Mannheim, Singapore) in 76 of them. Most patients (93%) were ethnically Chinese, predominantly males (74%) and chronic hepatitis B (72%) patients. Others had chronic hepatitis C (19%) or cryptogenic cirrhosis (6%). Four patients had acute non A-E hepatitis. HGV RNA and anti-HGenv were present in 3.5% and 8.3% of those with chronic liver disease. HGV infection did not account for any of the acute non A-E hepatitis and most of the cryptogenic cirrhosis.