The dexamethasone suppression test (DST) has been used in psychiatric pathology for about 10 years. Carroll et al. consider this test to be specific of endogenous depression. According to these, and many other authors, approximately 55% of patients with endogenous depression show a positive response to the test, whereas a positive response is observed in only 4% of normal subjects or patients with psychiatric disorders other than major depressive disorders. The DST was performed in 162 psychiatric inpatients (5 with organic disease, 28 with schizophrenic disorders, 17 with major affective disorders, 5 with obsessive compulsive disorders, 103 with dysthymic disorders and 4 unclassified). Dexamethasone (1 mg) was administered orally at 11 p.m., and plasma cortisol concentration was measured the following day at 16 p.m. Response to the test was positive in 53% of patients with major affective disorders, 25% of those with schizophrenic disorders, 60% with obsessive compulsive disorders and 18% with dysthymic disorders. There was no statistical difference in the results according to age, sex ratio, family history of depression or duration of the disorders. Only two variables were close to the P less than 0.05 level of statistical significance: severity of the disorders and early morning awakening. DST sensitivity, therefore, would appear to be about 50% in major affective disorders, but this test is not specific as it may also be positive in other psychiatric disorders. A positive dexamethasone suppression test may be regarded as a sign of severity of psychiatric disorders.