One hundred seven patients (77 women and 30 men) with migraine headache were given prophylactic treatment with timolol maleate, 20 to 30 mg/day, or matching placebo during a 20-week, double-blind crossover study. Among the 94 patients who completed the study, timolol was significantly better than placebo in terms of decrease in frequency of headaches from baseline, numbers of patients who had a 50% reduction in headache frequency, global response, and patient preference. Overall global response rates were 65% with timolol compared with 40% with placebo. The severity and duration of headaches that occurred were unchanged. Few side effects were reported with either timolol or placebo. The study demonstrates that the β-blocker timolol is a safe and effective treatment in patients with frequent migraine headaches.