The rewarding properties of systemically administered heroin were investigated with a conditioned place-preference paradigm. Reinforcing effects were observed with all doses of heroin tested (0.5, 1.0, 2.0 mg/kg) as indicated by a significant increase in preference for the place paired with drug injections. No similar change in preference was observed following saline injections. The rewarding effect of heroin (2 mg/kg) was attenuated by pretreatment with haloperidol (0.2 mg/kg), but haloperidol alone did not produce a place aversion. Lesions induced by 6-hydroxydopamine (6-OHDA) of the mesolimbic dopaminergic pathway at the level of the nucleus accumbens also attenuated the heroin-induced place preference. In contrast, depletion of central and peripheral noradrenaline induced by 6-OHDA had no significant effect on heroin-induced place preference. These data suggest an important role for the mesolimbic DA system in mediating the reinforcing effects of heroin.