Several methods of quantitative analysis were applied to the left parietal ‘resting’ EEGs of 48 nonpatient controls and 90 undrugged psychiatric inpatients. Patient and control groups, matched for age and sex, differed as follows: (a) Mean frequency was lower and frequency variability was greater in the total patient group than in controls. (b) Mean amplitude was higher and mean frequency lower in chronic schizophrenics than in controls; the amplitude differences were contributed mainly by female patients. (c) Amplitude and frequency means of nonpsychotic patients were intermediate between those of chronic schizophrenics and controls. (d) Mean amplitudes were greater and frequency variability was less in neurotics than in contr