ABSTRACTThe study of the dexamethasone suppression test (DST) in 374 chronic psychiatric patients with concurrent substance dependence, including alcohol, found 97% of nonsuppression associated with affective disorders. The incidence of nonsuppression was 38.5% in major depressive disorder and 27.7% in bipolar affective disorder. This study found no apparent connection between the incidence of nonsuppression and any particular drug group. Predex amethasone plasma concentrations were higher in affective disorders than in other diagnoses. It is concluded that the DST may be of value as part of the clinical approach to the diagnosis of major depressive disorders in a substance-abusing population.