BACKGROUND: Buprenorphine/naloxone (BUP/NX) is not licenced for use in China or Thailand and there was little clinical experience with this drug combination in these countries at the inception of HIV Prevention Trial Network (HPTN) 058, a randomized trial comparing risk reduction counselling combined with either short-term or long-term medication assisted treatment with BUP/NX to prevent HIV infection and death amongst opioid-dependent injectors. METHODS: We conducted a safety phase that included the first 50 subjects enrolled at each of the three initial study sites (N=150). Clinical and laboratory assessments were conducted at baseline and weekly for the first 4 weeks. Changes in laboratory parameters were estimated with random effects models. RESULTS: BUP/NX was well tolerated by study subjects and opioid withdrawal scores decreased substantially during the 3-day induction. Two participants experienced grade 3 clinical adverse events, which were categorized as probably not related to the study drug. Grade 2 or 3 increases in alanine aminotransferase (ALT) occurred in 25 (17%) subjects. The magnitude of ALT increase over 4-week follow-up was strongly associated with baseline ALT elevation. CONCLUSIONS: In Chinese and Thai opioid-dependent injectors, we found BUP/NX to be effective in reducing opioid withdrawal symptoms and safe during short-term use. ALT increases were observed over 4-week-follow-up, which are consistent with reports from Western populations. Long-term safety and efficacy evaluations are indicated.