In this dose-ranging, randomised, multinational, multicentre, double-blind, placebo-controlled, parallel group study, 431 patients treated a single migraine attack with study medication: sumatriptan suppository 6 mg, 12.5 mg, 25 mg, 50 mg, 100 mg, or placebo. Patients were treated in the clinic with a single dose in suppository form. All doses of sumatriptan, except 6 mg, were significantly better than placebo (p < 0.004) and achieved similar rates of headache relief within two hours of dosing. The highest response rate was in the 25 mg group (72%) compared with placebo (37%) (p < 0.001). Fewer patients required rescue medication in the active groups (1% 100 mg to 13% 6 mg) compared with placebo (17%), and more patients were able to work and function normally two hours after dosing (41%, 100 mg; 20%, placebo). The overall incidence of adverse events was similar in the placebo, 6 mg and 12.5 mg groups (14-17%) but higher in the 25 mg, 50 mg and 100 mg groups (25%, 32% and 29% respectively). Analysis of plasma sumatriptan levels indicated rapid rectal absorption for all doses (median tmax = 1.0 hr). It is concluded that sumatriptan, in doses above 6 mg, is an effective and well tolerated treatment for acute migraine. From this study doses of 12.5 mg and 25 mg sumatriptan were identified as having the best efficacy/safety profile and were evaluated further.