Harm reduction strategies for the prevention of transmission of human immunodeficiency virus (HIV) transmission among injecting drug users (IDUs) have been widely implemented in Australia and are seen to have been effective in preventing the spread of HIV. A major strategy has been increasing the availability of and accessibility to methadone maintenance therapy (MMT) programmes. We have reviewed the experience of a major MMT general practice with hepatitis C virus (HCV) infection from 1991 to 1995. Of 1741 individuals tested for HCV antibodies at least once 66.7% were positive. Of 73 IDUs who were initially seronegative and were retested at least once, 19 were subsequently seropositive. Seroconverters to HCV were younger than non-seroconverters, and were more likely to have evidence of previous hepatitis B infection. The overall HCV incidence rate was 22 cases per 100 person-years, and this did not differ between those on MMT programs (continuous or interrupted) between HCV tests and those not on MMT. These findings suggest that the role of MMT in the control of the spread of HCV infection among IDUs needs further assessment, and that control of the current epidemic of HCV infection among IDUs in Australia will be very difficult.