The efficacy of the 5-HT1 receptor agonist sumatriptan in the acute treatment of migraine has been investigated in an extensive programme of controlled clinical trials. Sumatriptan provided rapid relief from migraine headache with onset of relief occurring within 10 min of a 6 mg subcutaneous injection and within 30 min of a 100 mg oral dose. Maximum benefit was observed by 2 h after the injection and 4 h after the oral dose. Sumatriptan also significantly decreased the incidence of associated migraine symptoms (nausea, photophobia, phonophobia) and the need for rescue medication. Sumatriptan was an effective treatment for migraine with and without aura and when used at any time during the attack. Oral sumatriptan 100 mg provided significantly greater pain relief and had a more rapid onset of action than two commonly used acute treatments for migraine. Efficacy is maintained in long-term use, with no evidence of tachyphylaxis or dependence. Sumatriptan, whether given sub-cutaneously or orally, is an effective long-term acute treatment for migraine.