In a multinational, placebo-controlled, double-blind, parallel-group study of oral sumatriptan (GR43175), given as a dispersible tablet, in the acute treatment of migraine, 149 patients were randomized to receive 100 mg sumatriptan and 84 to placebo. Each patient was provided with three tablets: one to be taken as soon as possible after headache onset; one to be taken 2 h later if the headache persisted and one to be taken if the headache recurred within 24 h. Patients recorded details of the attack and response to treatment on a diary card. Sumatriptan was significantly more effective than placebo in relieving headache (moderate/severe reduced to mild/none) at 2 h (50 vs. 19%; p < 0.001) and at 4 h (75 vs. 30%; p < 0.001). Of the sumatriptan group, 59% took the second dose compared with 80% of the placebo group (p < 0.001). Compared with placebo, more patients on sumatriptan were pain-free by 2 h(26 vs. 5%; p < 0.001) and by 4 h(48 vs. 13%; p < 0.001). Headache improvement was apparent by 1 h in 42% of sumatriptan-treated patients and 17% of patients on placebo. Headache relief was significantly (p < 0.001) better in patients taking sumatriptan, irrespective of the type of migraine (with or without aura), or the time the drug was taken (less than or more than 4 h after onset). There was no significant difference in the number of patients who took placebo or sumatriptan and whose headache recurred within 24 h of initial resolution (42 vs. 48 %; p = 0.535). Accompanying symptoms of nausea, vomiting, photophobia and phonophobia were significantly (p < 0.001) improved in the sumatriptan-treated group. Sumatriptan was well tolerated; 38% of sumatriptan-treated patients reported one or more events compared with 23% in the placebo group (p = 0.019). Most of these events were minor and transient in nature. The occurrence of adverse effects was not dose-related and no significant effects were observed on heart rate, blood pressure, electrocardiogram (ECG), or biochemical or haematological parameters. It is concluded that a repeat-dose oral regimen of sumatriptan provides an effective acute treatment for migraine, while allowing patients considerable flexibility in the treatment of individual attacks.