The synthetic-work technique has been employed in a series of investigations designed to determine (a) the extent to which performance efficiency is degraded during extended periods of continuous work, and (b) the amount of sleep necessary for the recovery of performance from the effects of continuous work and sleep loss. The results of these studies indicate that 36, 44, and 48 hr of continuous work and sleep loss result in decrements in over-all work efficiency of approximately 15, 20, and 35% respectively. Following 36 hr of continuous work, it was found that 12 hr of sleep is sufficient for complete (100%) recovery of performance, but complete recovery is not provided by 2 (58% recovery), 3 (53% recovery), or 4 (73% recovery) hr of sleep. It also has been indicated that the time course of recovery is different following different durations of continuous work and subsequent sleep.