One hundred and twenty-four migraineurs were treated randomly with 5-hydroxytryptophan (5-HTP) or with methysergide (M). The two groups were homogeneous without significant statistical differences with respect to age, sex, pill use, type of migraine and frequency of attacks before entry. A significant improvement was observed in 75% of the patients treated with M and in 71% of the cases treated with 5-HTP. The most beneficial effect of 5-HTP appears to be felt with regard to the intensity and duration rather than the frequency of the attacks. Side effects were more frequent in the M group than in the 5-HTP group. These results suggest that 5-HTP could be a treatment of choice in the prophylaxis of migraine.