THE FUNCTION of dreaming and its relation to mental illness have recently become more amenable to laboratory investigation because of the discovery of reliable physiological indices of dreaming. Aserinsky, Kleitman, and Dement demonstrated that dreaming regularly occurs during discrete sleep periods characterized by intermittent bursts of conjugate rapid eye movements (REM) and a low voltage desynchronized electroencephalogram pattern (emergent stage 1).1-3 In the human adult REM sleep alternates with nonrapid eye movement sleep (NREM) in a cycle of approximately 90 minutes, during which REM sleep typically follows NREM sleep.2 Each night REM sleep occurs about four to six times in successively longer periods lasting 10 to 40 minutes and it occupies about 25% (100 minutes) of total sleep time.2.4 The unexpected finding that such abundant dreaming occurs at regular intervals every night strengthened the hypothesis that dreaming might be essential