Decreased slow-wave sleep (SWS) and sleep continuity are major effects of healthy aging and of associated psychopathological states. Using sleep deprivation, we studied the extent to which age- and psychopathology-related sleep "decay" is reversible in aged normal, depressed, and demented subjects. Depression or probable Alzheimer's dementia compromised the augmentation of sleep continuity and SWS seen in healthy elderly following sleep deprivation. Rapid eye movement (REM) latency decreased during recovery sleep in the controls but increased in both patient groups. Compared with demented patients, depressed elderly had greater severity of sleep continuity disturbance both before and after sleep deprivation, a more protracted course of recovery sleep, and increased slow-wave density in the second non-REM (NREM) sleep period (during recovery). The REM sleep time was diminished in dementia compared with depression both at baseline and during recovery sleep. These differential effects of age, health, and neuropsychiatric disease on recovery from sleep loss are relevant to recovery or reversal theories of sleep and have implications for daytime well-being in the elderly.