Nitroglycerin, a vasodilating agent, was administered sublingually in migraine without aura patients and in healthy volunteers. Systolic, diastolic and time-mean flow velocity and pulsatility index, were measured by transcranial Doppler sonography in the major intracranial arteries before and after nitroglycerin administration. Following nitroglycerin administration, a significant decrease in systolic and time-mean velocity and pulsatility index was observed in migraine patients, whereas in control subjects only time-mean velocity decreased significantly. Based on those findings we hypothesize a more marked responsiveness to nitroglycerin in migraine patients as compared to healthy subjects.