Four experiments on the effects on performance of extended time periods without sleep and on the effects of limited sleep, that is, naps, within such periods are reviewed. The performance measures included subjective measures and measures of performance on attention/persistence, continuous-production, precision, and cognitive tasks. Repeated periods of sleep deprivation did not result in decreased effects: Older subjects tended to be more vulnerable to sleep-loss decrements, and three different schedules of 4 h of sleep within a 60-h sleep-deprivation period had limited differential ameliorative effects.