Twenty-six patients with migraine attacks were treated for 3 to 16 months with flufenamic acid (125 mg four to six times per attack), an inhibitor of prostaglandin synthesis and action. In 25 patients the drug afforded symptomatic relief in 195 of 200 treated attacks. Side effects observed were mild dyspepsia (eight patients) and severe upper gastrointestinal symptoms (two patients). None of the eight patients treated with placebo reported any relief (20 attacks). The "common" antimigraine drugs afforded symptomatic relief in 12 of the patients, partial relief in seven, and no relief in seven. Treatment with flufenamic acid was based on the hypothesis that prostaglandins are involved in migraine attack and that the drug relieves migraine by inhibition of the vasoactivity of prostaglandins.