ACTH has been reported to decrease elevated levels of dopamine metabolites in the CSF of patients with infantile spasms who respond clinically to ACTH therapy. To study the possible role of dopamine receptors in the effect of ACTH, we treated rat pups for thirty days with 40 IU/kg subcutaneously of porcine ACTH or with normal saline. Using 10 nM 3H-spiperone and sulpiride to determine nonspecific binding, specific binding of D-2 receptors increased significantly (46%) in the striata of ACTH-treated rats when compared to controls. No significant difference in specific binding was found in the nucleus accumbens. Protein concentration was significantly decreased by ACTH treatment. Saturation studies will be necessary to determine if the increase in dopamine receptor binding induced by a high dose of ACTH represents a change in receptor density or affinity. The effect of lower clinical doses of ACTH on dopamine receptors warrants study.