The structure of nocturnal sleep was studied in two groups of subjects: the group I subjects had been given 60 unfamiliar English words to learn, whereas Group II subjects had been playing games of chess. The paradoxical sleep (PS) latency in the 1 st cycle, the type of falling into the PS, and intensity of rapid eye movements were recorded. No reliable difference was found in the sleep structure of both test groups. No correlation either was observed between the sleep characteristics and the quality of memorizing the verbal material.