The injecting behaviour and risky needle use of a sample of 193 methadone maintenance clients was investigated. The majority of the sample (n = 116) reported injecting one or more drugs in the month prior to data collection. Compared with non-injectors, the injectors were slightly younger, had been on the methadone program for a shorter period of time, had lower methadone doses and more severe drug and legal problems. The injecting sub-group was examined in more detail by comparing those subjects whose injecting practices conformed to guidelines on minimizing risk of HIV transmission with those who, in the preceding month, made at least one injection contravening these guidelines and thus placed themselves at risk of contracting HIV. A greater proportion of these risky injectors were unemployed. Importantly, risky injectors had lesser knowledge of means of preventing the spread of HIV than safe injectors. It is concluded that the reduction of HIV transmission could be enhanced by improvements in methadone programs, particularly ensuring adequate dosing and high retention rates. Further, there is a need to improve knowledge with regard to what are safe and what are risky injecting practices and needle/syringe cleaning methods.