A double-blind, placebo-controlled multicentre study was carried out to evaluate the efficacy and tolerability of 100, 200 and 300 mg sumatriptan, a selective 5-hydroxytryptamine (5-HT)₁-like receptor agonist, given in an oral dispersible form in the acute treatment of migraine attacks. A total of 1130 patients were recruited from 51 centres in eight countries and the efficacy results are presented from an interim analysis of 538 cases. Tolerability was evaluated in 227 patients. At 2 h, an improvement in headache severity from moderate or severe to mild or none was reported by 67% of patients who received 100 mg sumatriptan, 75% receiving 200 mg and 69% of patients receiving 300 mg sumatriptan, compared with 22% of patients who received placebo (P < 0.001="" all="" doses="" sumatriptan="" vs="" placebo).="" adverse="" events="" were="" generally="" mild="" and="" transient,="" and="" appeared="" to="" be="" dose-related;="" the="" adverse="" event="" profile="" of="" 100="" mg="" sumatriptan="" was="" similar="" to="" that="" of="" placebo.="" overall,="" nausea/vomiting="" and="">bitter taste were the most common complaints. The proportion of patients withdrawn due to adverse events was similar in the placebo and 100 mg sumatriptan treatment groups (2% and 3%, respectively). It is concluded that 100 mg sumatriptan given orally is well tolerated with an anti-migraine efficacy comparable to that provided by the two higher doses.