To evaluate the replicability of our previous findings of increased incidence of biological dysregulation in endogenous depression, we have studied a new series of patients with major depressive disorder, unipolar type (n = 103). The subtypes compared were defined by Research Diagnostic Criteria and were endogenous/nonendogenous, primary/secondary, and Winokur's family history classification. As an extension of the research, we evaluated the endogenous subtype more precisely by distinguishing those patients who met criteria for probable endogenous, comparing them to both endogenous and nonendogenous depressed patients. The findings of the replication study were consistent with our earlier report; the incidence of both dexamethasone nonsuppression and reduced rapid eye movement (REM) latency was higher in those with endogenous depression. Findings for each of the other subtypes revealed no differences. The probable endogenous depressed patients were comparable to the nonendogenous depressed patients in all variables measured.