The potential prophylactic value of a daily dose of 10 mg flunarizine, a calcium antagonist with anti-vasospastic properties was studied in a 3-month double-blind placebo-controlled trial in 58 migraineurs. With an almost perfect mutual correlation, both the patients' overall appreciation of the treatment and the reduction of migraine attacks proved flunarizine to be effective (p<0.001). Half of the flunarizine-patients considered the treatment certainly beneficial in contrast to none of the placebo-patients. In 21 of the 29 flunarizine-patients the attack rate was lower than expected in 20 of the 29 controls it was not. Younger patients appeared to respond better to the treatment. Flunarizine displayed a gradually increasing effect; during the third month 83% of the treated patients were completely attack-free. The drug did not appear to influence the severity and duration of attacks, however. Treatment was very well tolerated. Flunarizine, therefore, appears to be a very suitable agent for migraine prophylaxis but it should be given for more than two months in order to obtain full effectiveness with this dosage.