Although sublingual buprenorphine is an effective treatment for opioid addiction, the medication itself has abuse liability and, in some countries, has largely replaced heroin as the opioid drug of choice. In response to the reports of diversion and abuse of sublingual (SL) buprenorphine, a potentially less abusable formulation of buprenorphine that contains naloxone is being marketed in several countries. However, the relative abuse liability of buprenorphine alone and the buprenorphine/naloxone combination in buprenorphine-dependent individuals is unclear. Preliminary data from a study funded by Schering-Plough Corporation suggest that the buprenorphine/naloxone combination, when given intravenously (IV), does indeed have less abuse liability than IV buprenorphine in buprenorphine-dependent individuals. In addition to IV abuse of buprenorphine, epidemiological data suggest that buprenorphine is widely abused by the intranasal (IN) route. However, no data exist on the abuse liability of either IN buprenorphine alone or the buprenorphine/naloxone combination. Several studies have shown that naloxone is an effective antagonist of opioid agonist effects when given intravenously, but it is not clear whether naloxone given intranasally is as effective as when it is given by other routes of administration. Some studies have suggested that they are equally effective (Loimer et al., 1994), but others have shown that naloxone given intranasally is less effective (i.e., has a slower onset of effects) than when given by other routes of administration (Kelly et al., 2005). How this may impact on the ability of naloxone to reduce the reinforcing effects of IN buprenorphine is unclear. The primary aim of the current study proposal is to compare the reinforcing effects of IN buprenorphine and buprenorphine/naloxone in IN opioid abusers who are maintained on SL buprenorphine using a study design parallel to that used in our recent studies of the abuse liability of IV buprenorphine and buprenorphine/naloxone. Placebo, heroin, and naloxone will be used as neutral, positive, and negative controls, respectively. Secondary aims are to compare the subjective, performance, and physiological effects of IN buprenorphine and buprenorphine/naloxone. Overall, this study will complement our investigations of IV buprenorphine products by allowing for a complete overview within the same laboratory self-administration model of both the intravenous and intranasal abuse liability of buprenorphine versus buprenorphine/naloxone in individuals maintained on buprenorphine. The primary aim of the study is to compare the reinforcing effects of IN buprenorphine and IN buprenorphine/naloxone in opioid abusers maintained on different doses of sublingual buprenorphine. Secondary aims of the study are to compare the subjective, performance and physiological effects of IN buprenorphine and IN buprenorphine/naloxone. IN-administered placebo (lactose powder), naloxone alone, and heroin alone will be tested as neutral, negative, and positive control conditions, respectively. Participants (N=12 completers) will reside on an inpatient unit (5-South) during a 7 to 8-week study. This research will provide useful information to clinicians treating opioid dependent individuals with buprenorphine, and importantly, will provide information about the abuse potential and effects of buprenorphine on multiple measures of human functioning.