Eighteen hyperprolactinaemic patients were orally treated for up to 16 months with pergolide mesylate, a new potent long-lasting dopaminergic ergot derivative. In all cases, Prl normalization (less than 25 ng/ml) was achieved at a once-a-day dose of 50-300 micrograms. All women recovered and/or exhibited normal menstrual function. Among the 6 women wishing to become pregnant, 4 of them conceived within 4 months; there were other causes for infertility than hyperprolactinaemia in the 2 other couples. A macroprolactinoma man experienced important improvement in well-being as well as objective regression of his visual fields defect. This suggests a shrinkage effect of pergolide on the tumoural process. Another man regained normal potency and normal testosterone within 2 weeks. While 10 patients were completely free of any side effect, 7 experienced transiently mild gastro-intestinal side effects or postural hypotension. Only one patient discontinued her treatment because of dizziness. The present study demonstrates the high potency, the good tolerance and the excellent efficacy of pergolide in the treatment of hyperprolactinaemia.