An unusual behavioral and cardiovascular reaction was observed during opioid blockade with naltrexone in a 32-year-old male who met DSM III-R criteria for post-traumatic stress disorder (PTSD). As part of an ongoing placebo-controlled investigation of the effects of naltrexone on laboratory and ambulatory blood pressure reactivity, this participant reported experiencing feelings of rage, explosive behavior, and other unpleasant symptoms. When compared to all other subjects (N = 24), this individual showed significantly greater effects of naltrexone on blood pressure reactivity during the laboratory stressor. His ambulatory blood pressures, when compared to placebo, were significantly increased during the 24-hr period following naltrexone. The unusual behavioral and cardiovascular responses following ingestion of naltrexone suggest an important role for endogenous opioids in adjustment to stress in this case of PTSD.