This is a Phase I, open-label (patient and trial doctor know what medication you are taking at any point in time during the trial), add-on trial in patients who are on stable sublingual (placed in the mouth under the tongue until it disolves) buprenorphine/naloxone maintenance therapy, to investigate the potential pharmacokinetic effect of multiple-dose TMC125 on buprenorphine and norbuprenorphine administered as buprenorphine/naloxone. The study population will consist of 16 HIV-negative opioid-dependent patients on stable individualized sublingual buprenorphine/naloxone maintenance therapy. Patients will first participate in a 2 weeks run-in period with supervised buprenorphine/naloxone intake. Subsequently, patients will receive TMC125 200 mg orally twice daily for 14 days added to their buprenorphine/naloxone treatment. During the treatment period from Day 1 to Day 14, the individualized buprenorphine/naloxone treatment will be continued with co-administration of TMC125. Full pharmacokinetic profiles of buprenorphine and norbuprenorphine will be determined on Days -1 and 14 up to 24 hours postdose. Full pharmacokinetic profiles of TMC125 will be determined on Day 14 up to 12 hours postdose. Pharmacodynamic assessments of symptoms of opiate withdrawal and excess will be performed. The short-term safety and tolerability will be assessed throughout the trial. Patients will firstparticipate in a 2 weeks run-in period with supervised buprenorphine/naloxone intake. Subsequently, patients will receive 2 tablets of 100 mg TMC125 twice daily for 14 days added to their buprenorphine/naloxone treatment. During the treatment period from Day 1 to Day 14, the individualized buprenorphine/naloxone treatment will be continued with co-administration of TMC125.