ALTHOUGH most investigators conceptualize rapid eye movement (REM) sleep as one of two distinct kinds of sleep,1,2 a body of opinion persists which holds that the REM sleep cycle may be part of a more general rhythm continuing during both waking and sleeping.3-10 Kleitman has discussed a "basic rest-activity cycle," reflected in the two alternating kinds of sleep, which may also be operative during waking.3,4 Globus has reported data on daytime naps which suggests that REM sleep tends to occur at the same clock times each day5,6 and Globus and Gardner have conceptualized REM "sleep" as a time-locked ultradian rhythm superimposed as a ripple on the slower moving circadian rhythm of waking and sleeping.7 Similarly, Friedman and Fisher have suggested that "the concept of a sleep dream cycle be amended to that of a 24 hour continuous cycle of drive accumula