The purpose of this study was establishing the effect of moderate exercise on EEG tracings in young epileptics. The model of graded exercise was 15-minute work on a cycle ergometer. The effect of the exercise on the pattern of simultaneously recorded EEG was compared with the effect of 3-minute hyperventilation. After testing a control group of 20 young subjects without evidence of organic brain damage or with this damage causing no epilepsy another group of 43 epileptics was studied. In none of these patients the intensity of changes in EEG increased during the exercise but evident EEG differences could be detected during different stages of the exercise in 28 patients with significant generalized discharges. It was found that during the exercise in nearly all patients the number of discharges decreased while during hyperventilation it increased. In 10 patients in this group a repeated rise in the number of discharges was observed immediately after the exercise which was connected usually with greater fatigue after the exercise. In the light of these results the authors conclude that moderate exercise inhibits rather seizure activity in EEG contrary to hyperventilation which increases these changes.