As a maintenance agent for opioid dependency, buprenorphine offers advantages such as a lower level of dependence and minimal withdrawal symptoms, due to its partial agonist properties at the micro-opioid receptor. Previous studies have shown 8 mg sublingual buprenorphine to be equivalent to 60 mg oral methadone in terms of retention rate and opioid-negative urine levels. In a 24-week, ongoing European study, 34 opioid-dependent subjects were assessed; 16 receiving buprenorphine and 18 methadone. A free dosing schedule was used with no upper limit for methadone dosing but with a maximum buprenorphine dose of 8 mg. Screening prior to the study excluded subjects with polysubstance dependence, somatic disease and/or HIV infection. Primary outcome measures were abstinence from other drugs, for which subjects provided weekly urine samples for analysis of opioids, cocaine and benzodiazepines, and retention in treatment. Patients in the buprenorphine group provided a greater proportion of negative urine samples, in particular cocaine-negative samples, compared with the methadone group, although this was not statistically significant. Retention in the buprenorphine group was significantly lower than in the methadone group, suggesting that the 8 mg buprenorphine limit may have biased the results in favour of methadone, and that this dose may have been too low for those subjects with high levels of dependence. However, buprenorphine is clearly effective in the more motivated subjects and further investigation in this subgroup is recommended.