Subcutaneous GR43175 was examined in patients with acute migraine for efficacy, tolerability and safety in an open, controlled, dose-ranging study. Ten patients with acute, non-medicated, migraine (15 attacks) were assessed for severity of headache and associated symptoms (nausea, vomiting and photophobia). GR43175 plasma samples were monitored serially after dosing. Doses of 2 mg or 3 mg gave rapid relief of all migraine symptoms. Thirteen attacks (86%) had either resolved completely or improved to a mild non-migraine residual headache within 40 min. Treatment was well tolerated at all doses, the only adverse effects being transient pain on injection. Peak plasma concentrations were obtained within 10-20 min; a decline in plasma drug concentration did not result in a relapse in headache severity.