Naloxone has been combined with buprenorphine to decrease the parenteral abuse potential of buprenorphine in opioid dependent individuals through the mechanism of naloxone-precipitated withdrawal. While naloxone will not precipitate withdrawal in individuals who are not physically dependent on opioids, it is possible naloxone might attenuate buprenorphine's agonist effects, especially if administered parenterally. The purpose of this study is to assess the effect of sublingual (SL) and intramuscular (IM) buprenorphine and buprenorphine/naloxone in non-dependent opioid abusers.