Benzodiazepines are used routinely in the treatment of sleep and anxiety disorders and, among IDUs, they improve the symptoms of opiate withdrawal. Studies have indicated that benzodiazepine misuse may have serious adverse physical and psychological effects, such as higher rates of injecting risk behavior, psychopathology, reduced health and social functioning, and greater risk of opiate overdose. The patterns of oral and intravenous benzodiazepine use among IDUs were examined in Melbourne and Hobart. The characteristics of IDUs that inject benzodiazepines were compared with those using orally. Samples of 152 Melbourne and 100 Hobart IDUs were recruited from needle and syringe program outlets and administered a structured survey on patterns of benzodiazepine use, injection-related health problems, and drug use history. Findings show that benzodiazepine use was common among the majority of IDUs surveyed, and that preferred types of benzodiazepines differed as a function of route of administration. The IDUs surveyed reported higher rates of both oral and intravenous use of benzodiazepines compared to other jurisdictions. Available evidence from other sources was suggestive of an apparent increase in the rates of benzodiazepine injection among IDUs in Melbourne and Hobart. Benzodiazepine injection for the Melbourne IDU respondents was significantly associated with recent experience of thrombosis, difficulty injecting, public injecting, and injecting equipment sharing. The only significant correlate of benzodiazepine injecting for the Hobart respondents was experience of a dirty hit. This may reflect the fact that most of the non-benzodiazepine injectors in the Hobart group were frequent injectors of pharmaceutical morphine and methadone--practices also associated with significant venous damage. 2 tables, 24 references