Parenterally transmitted non-A, non-B (NANB) hepatitis virus or hepatitis C virus is a common cause of both acute and chronic hepatitis. Using a recently developed enzyme-linked immunosorbent assay we looked at the prevalence of antibodies to hepatis C virus (anti-HCV) in a number of groups. People with haemophilia (75.6%) and intravenous drug users (61.9%) had the highest prevalence, while homosexual men attending a sauna (34.1%) and prisoners (30.8%) had a moderately high prevalence of anti-HCV. A lower prevalence of antibody was detected in female prostitutes (10.4%), institutionalised mentally retarded subjects (9.5%), homosexual men requesting human immunodeficiency virus (HIV) testing through their local doctor (8.8%), dialysis patients (5.9%), renal transplant patients (6.9%), and patients referred from a sexually transmitted diseases clinic (6.2%). The lowest prevalence of anti-HCV was recorded in women attending a provincial hospital for antenatal care (0.4%). The predominance of anti-HCV in groups of people exposed to blood-borne and sexually transmitted infections suggests that these routes may be primarily involved in the spread of hepatitis C virus infection.