- The purpose of this study was to test the hypothesis that minor EEG abnormalities predict a favorable response to clozapine. Eighty-six psychotic clozapine-treated psychiatric inpatients with EEG records before starting clozapine were included in the study. When all diagnostic groups were combined, there were no significant differences in clinical outcome between patients with abnormal EEGs and patients with normal EEGs. However, female patients with abnormal EEGs had a significantly greater improvement in Global Assessment of Functioning (GAF) scores compared to female patients with normal EEGs. In addition, patients with major depressive episodes (bipolar, schizoaffective, unipolar) and abnormal EEGs had a significantly greater improvement in GAF scores compared to the same subgroup of patients with normal EEGs. The results suggest that EEG abnormalities before clozapine treatment many predict a favorable clinical response in specific groups of patients.