The sigma1 (sigma1) receptor constitutes a particular target of cocaine believed to be involved in some of its behavioral effects. In the present study, its involvement in the rewarding effect of cocaine was examined using the conditioned place preference (CPP) procedure. CPP was induced in C57Bl/6 mice injected repeatedly with cocaine (20 mg/kg, i.p.). The selective sigma1 receptor antagonists NE-100 and BD1047 (1-10 mg/kg, i.p.) significantly attenuated or blocked the cocaine-induced CPP. Animals treated centrally with a sigma1 receptor antisense oligodeoxynucleotide failed to develop cocaine-induced CPP, unlike mismatch controls. The sigma1 receptor thus appears to be critically involved in the development of the cocaine-induced CPP and, in consequence, may constitute a promising approach to blocking cocaine reward.