The efficacy in acute migraine of oral sumatriptan was assessed in a double-blind, randomised, placebo-controlled, crossover study of 61 patients (mean age 39 [SD 10] years). 41 completed treatment of four attacks, two with sumatriptan 100 mg and two with placebo. The response rate (reduction in headache from moderate or severe to mild or absent at 2 h) was 51% (45/89) with sumatriptan and 10% (9/93) with placebo (p < 0.01); rescue medication was needed at 2 h in 41% and 88%, respectively. Of 28 patients headache-free at 2 h, 11 (39%) had recurrent headache within 24 h. There were no substantial side-effects. Thus, sumatriptan is an effective well-tolerated treatment for acute migraine attacks.