Electroencephalographic changes occurring in patients with migraine have received much attention. Although in migraineurs a number of studies have been done after nitroglycerin-induced attacks, there is no reported EEG study before and after nitroglycerin-induced sumatriptan-treated attacks. We, therefore, studied the EEG topographic frequency analysis in 19 symptom-free, otherwise healthy, unmedicated patients with common migraine and in 19 age- and sex-matched controls before nitroglycerin, at the time of maximum pain, and 30 minutes after sumatriptan. During headache attacks, an increase of slow rhythmic activity of the theta and delta range and a decrease of activity in the alpha and beta range were observed. These abnormalities disappeared 30 minutes after a sumatriptan injection. This suggests that common migraine is associated with disturbances of cortical electrogenesis and may provide insight into the causes of migraine and aid in the development of effective therapies.