Ten patients with psychotic depression were assessed on a battery of clinical, EEG, psychological, and biochemical measures during treatment with imipramine (150 mg/day). Significant changes occurred in the scores on self-rated and observer-rated depression scales and on an observer-rated side effect scale. Significant changes also occurred in the EEG evoked response, but the effects on spontaneous activity were minimal. The psychological measures revealed an improvement in performance as treatment progressed. The clinical significance of the changes observed was assessed with reference to their correlations with the clinical rating scores and with the plasma concentrations of imipramine and desmethylimipramine, and the changes observed following the administration of imipramine to non-depressed normal subjects. Changes in evoked EEG activity seemed on balance to be direct central effects of imipramine, whereas changes in psychological performance appeared to be secondary to clinical change.