Buprenorphine is an important alternative to methadone in the maintenance treatment of heroin addiction. Transfer from methadone to buprenorphine requires a reduction of daily methadone dosage below 30 mg to avoid withdrawal after the first buprenorphine intake. The study hypothesis states that the transfer from a daily methadone dosage between 60 mg and 100 mg to buprenorphine can be carried out without withdrawal using buprenorphine patches (35 micro grams per hour) within 12 to 48 hours after last methadone intake.