Psychobiological research has been used to validate subtypes of affective disorder. Nosologic separation of delusional from nondelusional depression has recently been aided by sophisticated analyses of sleep electrophysiology. In the present study, the sleep of elderly delusional and nondelusional depressed patients could be successfully distinguished from that of aged controls using standard sleep parameters. However, only a combination of manual and spectral analytic techniques separated the depressive subtypes. These results are preliminary and need replication in a larger sample.