As many as 30 patients with affective psychoses were examined for the concentration of plasma kynurenine, a neuroactive tryptophan metabolite, and for the parameters of the dexamethasone test. A group of patients suffering from "endogenous anxiety" and endogenous depression were distinguished. In the patients' group with "endogenous anxiety", the concentration of kynurenine at the height psychosis was significantly higher as compared to controls, correlating with the gravity of anxious symptomatology. In the patients' group with endogenous depression, plasma kynurenine was significantly lower than in controls but did not agree with the depression gravity. The dexamethasone test appeared pathological only in the group of patients suffering from endogenous depression and its parameters correlated well with the gravity of depressive symptomatology. In both groups, the study parameters returned to normal after the egress from the morbid condition.