Rats trained to intravenously self-administer cocaine hydrochloride on a fixed ratio-5 schedule were subjected to a series of systemic injections of the D1 dopamine receptor selective antagonist SCH 23390 and the D2 dopamine receptor selective antagonist spiperone. SCH 23390 produced a dose-dependent increase in cocaine intake at doses of 5, 10 and 20 micrograms/kg, but the D2 antagonist failed to reliably increase responding except at a dose of 10 micrograms/kg. These results suggest that the D1 antagonist may be more effective at blocking mesolimbic dopamine activity, and that selective D1 receptor activation may be an important component of psychostimulant reward.