Propranolol penetrates the blood brain barrier, whereas mainly the racemic form, Inderal, possesses beta-receptor blocking properties. A comparison between d-propranolol and Inderal might therefore indicate the relative importance of the beta blocking properties and possible "central" effects mediated by propranolol and of importance in migraine prophylaxis. The effects of propranolol in racemic form (Inderal) 40 mg q.i.d., d-propranolol 40 mg q.i.d. and placebo were compared in 20 migraine patients. Inderal as well as d-propranolol were significantly superior to placebo. Inderal seemed to be more effective than d-propranolol, but the difference was not statistically significant (P greater than 0.05). The results indicate that beta-receptor blocking properties, but possibly also properties other than the beta-blocking ones, may be of importance for the anti-migraine effect of propranolol.