A dopaminergic agonist, piribedil, was administered by intravenous infusion (0.1 mg/kg over 30 minutes) to 20 patients known to suffer from migraine and 20 subject free from any kind of headache. Neither changes in cerebral blood flow (CBF), as measured by the 33Xenon inhalation technique, nor peripheral side-effects were noted in the control group. Patients with migraine exhibited an 18 p. cent increase in CBF and a 32 p. cent decrease in mean arterial pressure and rapidly developed nausea severe enough to discontinue the infusion in most cases. Prior administration of domperidone, a neuroleptic drug which does not cross the blood-brain barrier, suppressed the nausea and fall in blood pressure but had no effect on the increase in CBF. This study confirms the existence of central and peripheral hypersensitivity to dopaminergic agents in patients with migraine. The piribedil test could be used to distinguish genuine migraine from ordinary cephalalgia in patients prone to headache.