A survey was undertaken in Sydney in 1989 to identify factors associated with behaviour involving risk for human immunodeficiency virus infection. Self-report data on needle-sharing and sexual practices were collected from 91 heroin users entering a residential, drug-free detoxification unit. Data were analysed using polytomous and ordinal logistic regressions. Heroin-dependent subjects who also had a current alcohol problem were significantly more likely than others to report high risk needle-sharing behaviour. Subjects with more than one sexual partner in the last three months were significantly more likely to use condoms while those with a current benzodiazepine problem were significantly less likely to use condoms. Qualitative data suggest that high risk needle-sharing behaviour most often occurred around the time of relapse to injecting drug use and among homeless drug users occupying derelict buildings in inner-city suburbs.