During 26 consecutive nights, electroencephalographic recordings and/or actigraphs were used to monitor the nighttime sleep of 10 asymptomatic healthy sleepers (mean age = 23.6 years). The schedule comprised: 7 nights of base line sleep, 14 nights of extended sleep (up to 10 hr/night), and 5 nights of recovery sleep. During extended sleep, subject1, slept significantly longer (approximately 1 hr), but sleep latency and interim wakefulness deteriorated. Extended sleep produced no improvements to sell-rated mood or subjective sleepiness. Vigilance tests showed a small but significant reduction in reaction time following extended compared with both baseline and recovery nights. Ability to detect target tones did not change significantly. Multiple Sleep Latency Test scores during extended sleep showed small (about 1 min) reductions. These findings give little support to the view of chronic sleep deprivation in the average 7.5-hr sleeper.