Ibopamine, diisobutyric ester of N-methyl dopamine, is an orally active dopaminergic agonist. The prolactin-lowering activity of Ibopamine was studied in 8 subjects with normal prolactine levels given the drug in a single dose of 100 mg. Prolactin levels measured by radioimmuno assay were evaluated before and within 2, 4 and 8 h of administration. Afterwards prolactin levels were evaluated after 4 and 8 days of treatment with Ibopamine administered at a dose of 50 mg three times daily. Ibopamine was shown to decrease prolactin to a statistically significant extent at the 2nd h after administration. At the 4th h prolactin returned to baseline values. After 4 and 8 treatment days prolactin levels did not differ significantly from baseline values. These results provide further evidence for the dopaminergic activity of Ibopamine and suggest a more through investigation in hyperprolactinemic subjects.