The problem of hereditary factors in epilepsy has long been an important one. Lennox, Gibbs and Gibbs1 pointed out that "only one epileptic person in five is able to name any relative who has been similarly affected." Yet these observers found abnormal electroencephalograms in 54 per cent of 138 relatives of patients with epilepsy. The relatives comprised parents, children and siblings. Löwenbach2 obtained abnormal electroencephalograms for 17 of 37 nonepileptic relatives of 2 epileptic patients. Strauss, Rahm and Barrera3 found abnormal electroencephalograms in 26.9 per cent of 93 relatives of 31 epileptic persons. PRESENT STUDY Electroencephalograms were obtained from 15 known epileptic patients and 36 of their nonepileptic relatives, consisting of 20 parents, 15 siblings and 1 maternal aunt. In all cases tracings were recorded during a period of quiet rest and during a six minute period of hyperventilation. None of the patients or relatives had a