Thirty-one patients with hyperprolactinemia were admitted for protocol study. Twenty-one of these patients had no findings of prolactinoma by computerized axial tomography (CAT) scanning; 10 had documented tumor by CAT scan. The patients were assigned to either Parlodel or Pergolide treatment on the basis of random numbers tables. They were treated for 6 months continuously and followed during this time with radiologic survey, hormonal evaluation, and blood chemistry determinations. Patients in both groups showed a decrease in prolactin levels, whether they were treated with Parlodel or Pergolide. The response was similar whether patients had hyperplasia or pituitary tumors. Patients with pituitary tumors tended to have a diminution in the size of their lesions regardless of the dopamine agonist used. The types of side effects experienced by various groups were similar regardless of the treatment. It is concluded that both Pergolide and Parlodel are useful in the treatment of hyperprolactinemic syndromes, although neither one appears to be superior to the other.