Rhesus monkeys were surgically prepared with chronic intravenous catheters and allowed to self-administer the indirect dopamine (DA) agonist cocaine (0.03 or 0.1 mg/kg/inj) or the direct D2 agonist piribedil (0.1 or 0.2 mg/kg/inj) on a fixed-ratio 10 schedule of drug delivery during daily 2 hour experimental sessions. When responding was stable, they were injected IV with SCH 23390, a selective D1 antagonist (0.003-0.3 mg/kg, 30 min pre-session) or pimozide, a selective D2 antagonist (0.003-0.3 mg/kg, 2 hours pre-session). Intermediate doses of pimozide generally increased self-administration of cocaine or piribedil, though increases in piribedil self-administration were more reliable. In contrast, intermediate doses of SCH 23390 either did not affect or decreased cocaine and piribedil self-administration. High doses of each antagonist decreased the rate of self-administration of each compound and produced catalepsy. The selective increase in responding maintained by cocaine or piribedil following pimozide pretreatment suggests a role for a D2-like receptor in psychomotor stimulant self-administration.