Baseline electroencephalographic (EEG) sleep and the EEG sleep response to scopolamine were studied in 10 adult female patients with unipolar major depressive disorder. Subjects were studied twice for two consecutive nights while depressed and, again, during remission. On the second night of each two-night session, normal saline or scopolamine (1.5 microg/kg, i.m.) was administered in a randomized, double-blind, cross-over fashion. Nocturnal urinary free cortisol (NUFC) measures also were collected. Compared to the depressed state, NUFC was significantly lower during remission. In contrast, baseline EEG sleep measures did not differ from episode to remission. Scopolamine suppressed rapid eye movement (REM) sleep to a comparable extent during the depressive episode and in remission. Scopolamine also reduced NUFC secretion during both clinical states, but to a lesser extent than REM sleep suppression. The findings suggest that the dysregulation in cholinergic systems associated with depressive illness may be persistent during remission, at least for some cholinergic systems. The results also suggest that the central cholinergic system(s) that regulate(s) REM sleep may be more sensitive to dysregulation than the cholinergic system(s) that control(s) nocturnal cortisol secretion.