Patients with migraine show a hypersensitivity to dopamine or its agonists. One of these, piribedil, was administered as 0,1 mg/kg intravenously over 30 minutes to 150 subjects with either migraine or other types of headache. This test provoked nausea and vomiting in 94 p. cent of patients with migraine, and a rapid fall in blood pressure requiring immediate interruption of the infusion in 69 p. cent. In contrast, in those subjects with chronic non-migrainous headache the administration of piribedil had no effect in 61 p. cent and provoked a fall in blood pressure in only 16 p. cent. The piribedil test appears to possess good specificity vis-à-vis migraine, enabling a differential diagnosis from atypical periodic headache, a condition difficult to consider as migrain or psychogenic headache on clinical grounds alone.