Almost all sleep-promoting drugs distort the natural pattern of sleep by suppressing rapid eye movement (REM) sleep, and cause a rebound to above-normal values on withdrawal which typically lasts about six weeks (Oswald, 1968, 1969). Furthermore, barbiturates reduce the number of eye movements per unit time in REM sleep (Oswald et al., 1963; Baekeland, 1967; Lester et al., 1968; Feinberg et al., 1969), with a rebound in eye movement (EM) profusion on withdrawal (Oswald, 1970). Non-barbiturate hypnotics do likewise, also with a rebound in EM profusion on withdrawal (Allen et al., 1968; Lewis, 1968).