A survey of 448 clients receiving opioid treatment in public clinics in Australia was conducted during 2005, exploring diversion and injection of supervised methadone and buprenorphine, frequency and reported effects of injecting, and the cost and availability of street-purchased pharmacotherapies. The rates of diversion in the preceding 12 months were over three times higher among participants receiving supervised buprenorphine (15.3%) than among those receiving supervised methadone (4.3%). While 26.5% of participants currently prescribed buprenorphine had ever injected buprenorphine, 65.9% of those prescribed methadone reported ever injecting methadone. The majority of participants did not appear to have extensive experience of injecting their medication and most expressed a preference for taking it as directed. Further research is required to determine the optimal approach for the supervised administration of buprenorphine that maximizes the benefits of treatment and minimizes harm and the risk of diversion. The study's limitations are noted.