The abnormal ϑ-rhythm of the EEG can be identified by use of spectral analysis. The rhythms appear as peaks in the power spectrum and can be considered as given, if the intensity of this peak is significantly higher than the average intensity and if a left-right coherence is present. Abnormal ϑ-rhythms in the parietal region are significantly more frequent in children with a history of febrile convulsions than in controls. This difference becomes especially obvious in the records with open eyes. According to previous investigations, the abnormal ϑ-rhythm is correlated with a genetically determined susceptibility to convulsio