In 26 patients with psychiatric disorders, EEG, and visual averaged evoked responses (VAER) were recorded. In the analysis of the EEG, the mean integrated amplitude (MIA), its within patient variance (WPV), and the coefficient of variation CV=(square root of WPV/MIA) X 100 were calculated. Patients were grouped as augmenters on reducers according to their tendency in the VAER recording to augment or to reduce the intensity of incoming signals with increasing stimulus intensity. The content of monoamine metabolites, 5-hydroxyindoleacetic acid, 5-HIAA, and homovanillic acid (HVA), and --for 17 patients-- tryptophan, in the cerebrospinal fluid was determined. In the analysis of the results, WPV in the alpha-band was found to be significantly correlated to HVA (r=0.45, p less than 0.02) and to 5-HIAA (r=0.34, p less than 0.05). In a multiple regression analysis, the correlation between WPV and HVA was found to be the most important. CV was found to be signfiicantly correlated to tryptophan (r=0.68, p less than 0.01). In the analysis of the results of the VAER, reducers were found to have higher levels of 5-HIAA and tryptophan and significantly higher values of HVA. The results are discussed in relation to earlier neurophysiological and biochemical theories about psychiatric patients.