The dopaminergic actions of various hallucinogenic drugs were assessed by examining their effects on turning behavior in rats with unilateral 6-hydroxydopamine lesions of the nigro-striatal pathway. LSD (0.1 and 0.2 mg/kg) produced strong contralateral turning, indicating that it is a potent dopamine receptor agonist, while BOL (5 mg/kg), a non-hallucinogenic congener of LSD, was found to be a weak dopamine receptor agonist. STP (2 and 5 mg/kg) and mescaline (50 and 100 mg/kg) produced significant ipsilateral turning, indicating that these compounds have a moderate dopamine-releasing action. DMT (10 and 20 mg/kg) and 5-M-DMT (0.75 and 1.25 mg/kg) produced weak ipsilateral turning, which was not significantly different from that produced by the nonhallucinogenic compounds tryptamine (40 mg/kg) or scopolamine (0.25 mg/kg). Psilocin (1-20 mg/kg) produced no significant turning in either direction. These data, in conjunction with previous studies, indicate that while inactivation of the brain serotonin system may be a necessary and sufficient condition for hallucinogenesis, the ability to activate dopamine receptors may be an important factor in determining the potency of hallucinogens.