The prophylactic effects of nadolol once daily and propranolol b.i.d. were studied in 28 patients with common or classic migraine. Following screening procedures, the subjects entered a 28- to 120-day placebo period, which was followed by a 24-week randomized, double-blind treatment period. The prophylactic effects were evaluated by frequency of migraine attacks, consumption of acute migraine-relief tablets, duration of attacks, ratings of headache and nausea severity, and duration of incapacitation. Compared to placebo, both beta blockers brought about a highly significant (p < 0.01 ) reduction in attack frequency and consumption of acute migraine-relief tablets, while no significant changes were found with regard to the other variables. No significant differences were found between the two beta blockers. The results indicate that nadolol once daily is as effective as propranolol b.i.d. in migraine management and that the main effect of beta blockers in migraine is in preventing attacks from breaking out, while the capacity for reducing the intensity or duration of unsuppressed attacks is less prominent.