Case studies reveal that opiate addicts often self-medicate with benzodiazepine (BDZ) tranquilizers prior to taking their opiate. Our laboratory has previously utilized the conditioned place preference paradigm to confirm that BDZs can augment the affective response to heroin in laboratory animals. The combination of alprazolam and varying doses of intravenous heroin resulted in a leftward shift of the heroin dose-response curve. The present experiment was devised to extend the previous findings by examining the ability of varying alprazolam doses (0.125, 0.25, or 0.5 mg/kg ip) to potentiate the reward of a single challenge dose of heroin (0.025 mg/kg iv). The results demonstrate that a nonrewarding dose of alprazolam (0.125 mg/kg) and intravenous heroin can interact to produce reliable place preferences. The data thereby support prior work from our laboratory regarding the synergistic actions of BDZs and opiates.