Plasma cortisol levels examined at 16.00 hours after dexamethasone in 31 controls and in 34 psychotic patients with various diagnoses, suggests that the ranges of such levels may help to discriminate among subtypes of psychotic patients. They were significantly higher in the unipolar depressed psychotic group than in control subjects or in psychotic patients with bipolar depression or schizophrenia. Moreover, the distribution of values differed between groups. Whereas 8 of 14 psychotic patients with unipolar depressive illness had post-dexamethasone cortisol values greater than or equal to 14 micrograms/dl, none of the remaining psychotic patients had similarly high values. Implications of these data are discussed.