Twenty-nine patients with macroprolactinomas were treated by monthly intramuscular injections of the long-acting and repeatable form of bromocriptine (Parlodel-LAR) in doses ranging from 50-150 mg. They were divided into two groups: group I consisted of 22 patients who received Parlodel LAR before transsphenoidal adenomectomy; group II was composed of 7 patients with earlier neurosurgery and of 2 patients from group I not cured by transsphenoidal adenomectomy. Duration of therapy varied from 1-12 months, and a total of 104 injections was given. At nadir day, serum PRL levels were situated between less than 1% and 43% of pretreatment values. At day 28 after the first injection, serum PRL levels varied between less than 1% to 139% of initial values. No difference could be detected between the two groups regarding the percent of PRL inhibition. Long-term treatment with Parlodel-LAR resulted in a sustained inhibition of PRL secretion, except for 1 case. Resumption of menstrual cycles occurred in 4 out of 15 women and correction of hypogonadism in 4 out of 14 men. Amelioration of disturbed visual fields was recorded in 3 out of 8 patients. Diminution of the adenoma volume was radiologically documented in 14 out of 22 cases. Only few and mild side effects were recorded. One patient with partial adrenal deficiency suffered from a syncope, but this was prevented by hydrocortisone supplementation during the subsequent Parlodel-LAR administration. In conclusion, Parlodel-LAR proved effective in the treatment of macroprolactinomas, achieving rapid inhibition of PRL secretion, and in some patients amelioration of hypopituitarism, reduction in tumor size, and improvement in visual fields, and caused no serious side effects. It is a valuable preparation to surgery and can also be used in long-term medical therapy.