Different weekly doses (400 to 3,000 micrograms) of the new, long-acting dopamine agonist Cabergoline (Farmitalia Carlo Erba, Milan, Italy) were given to 11 hyperprolactinemic women with pituitary tumor. Pituitary computerized tomography (CT) scans were performed before the start of treatment and after 3 (n = 5), 6 (n = 3), and 9 (n = 3) months of Cabergoline administration. Plasma prolactin (PRL) was determined in blood samples collected before and at weekly intervals during Cabergoline administration. Cabergoline induced marked inhibition of PRL secretion in conjunction with a CT demonstration of reduction in the pituitary tumor size in all patients. The potent, long-lasting PRL inhibitory effect of Cabergoline and the absence of side effects typical of dopaminergic compounds suggest that the use of this drug is advantageous over others in the medical treatment of hyperprolactinemia.