The effect of Vincamine and Piracetam, two geriatric drugs, on sleep behavior of the laboratory cat was studied. The animals were chronically prepared for recording of the EEG of the cerebral cortex, the lateral geniculate body, and the hippocampus, and for recording of eye movements, the muscular tonus and respiration. During the experiment, sleep and waking behavior were monitored by the above mentioned telemetrically transmitted indicators and also through observation via closed-circuit television. Both Vincamine and Piracetam in doses of 1 and 300 mg/kg p.o., respectively, enhance absolute and relative amounts of paradoxical sleep (PS). Smaller doses have a lesser or no effect on PS. Larger doses again have little effect or else, in the first few hours after application, reduce PS and total amount of sleep. Both drugs have little effect on slow wave and total sleep. Piracetam, but not Vincamine, reduces the prominent frequency of the theta band in hippocampus during PS. The PS-enhancing effect of the two geriatric drugs may be related to their memory-improving influence.