Buprenorphine is a drug that may be helpful in treating opioid dependent individuals who were previously maintained on methadone. The purpose of this study is to determine the effects of different doses of buprenorphine/naloxone in treating opioid dependent individuals who were previously maintained on methadone.

Buprenorphine is a mixed agonist-antagonist opioid that is being developed as a treatment for opioid dependence. Because buprenorphine is a partial mu agonist opioid, under certain conditions it is possible for buprenorphine to precipitate opioid withdrawal in opioid dependent individuals. A person with a high level of physical dependence could experience buprenorphine-related precipitated withdrawal. The purpose of this study is to test the acute effects of different doses of buprenorphine/naloxone in opioid dependent individuals maintained on methadone. The study is designed to provide dosing schedules similar to those that might be initially used in a physician's office.

Inclusion Criteria:

• Meets criteria for opioid dependence

Exclusion Criteria:

• Significant medical or psychiatric illness