The authors administered methysergide maleate to 421 patients who previously had been treated, without success, for recurrent headaches over periods as long as 55 yr. The drug was given in amounts ranging from 6 to 16 mg per day in divided doses. The treatment, essentially prophylactic, was continued for periods up to 29 mo. Side effects were frequent and adjustment of dosage was necessary. The data led to the conclusion that methysergide maleate has no value in treating the acute attack, but is effective in the prophylactic treatment of all forms of migraine headache.