Adrenocorticotropin (ACTH) levels in plasma increased rapidly to 105% above baseline within 5 minutes after intravenous injection of cocaine (30 mg) in cocaine-dependent men. The time course of ACTH stimulation paralleled increases in plasma cocaine levels and self-reports of salient drug effects on mood states and did not occur after placebo administration. An opioid mixed agonist-antagonist, buprenorphine (4 mg/day sublingually), suppressed the acute cocaine-induced stimulation of both ACTH and euphoria. Buprenorphine's suppression of postcocaine ACTH and euphoria were not related to differences in plasma cocaine levels or cocaine-induced alterations of cardiovascular function.