Lysergic acid diethylamide (LSD) has a number of reasonably well established general effects upon operant behavior. Transient interruption of responding ("pausing) has been observed in rats (Appel and Freedman, 1964; Freedman et al, 1964, Liberson, Ellen, Schwartz, Wilson, and Gagnon, 1962, Olds and Olds, 1964; Ray, 1965) guinea pigs (Liberson et al, 1962) pigeons (Berrymand, Jarvik and Nevin, 1962), and rabbits (McGaugh, De Baran and Longo 1963). The tasks involved included responding for food on simple schedules of reinforcement, hypothalamic self-stimulation, approach behavior and complex discrimination learning (matching to sample). Similarly, depression or lowering of respons rate has been seen in monkeys (Jarvik and Chorover, 1960), rats (Jarrard, 1963; Freemand et al, 1964; Ray, 1965), humans (Osterfeld, 1961) and pigeons (Blough 1957a). As would be expected, increase in reaction time is another common finding with LSD (Berryman, et al 1962; Edwards and Cohen, 1961; Fuster, 1957, 1959). Tolerance to the behavioral effects of LSD has also been investigated (Freeman et al, 1964).