8 Ss were presented verbal stimuli (numbers) during different stages of sleep. 15 sec. after each presentation they were awakened and asked if they had heard anything. If not, they were presented a multiple-choice test including the stimulus and another 3 numbers. It was concluded that: (1) even during stages 3 and 4 some perception of verbal stimuli is possible during sleep; (2) there is a progressive blurring of perception from stage 1 and REM to stages 3 and 4; (3) some forms of learning seem to be possible during sleep beyond a drowsy state, e.g., associations of words, but perceptual distortions make extremely unlikely the assimilation of complex verbal materials. It was also noticed that most verbal stimulations tended to produce a lightening of sleep as measured by the EEG. Based on the responses of some Ss the possibility of some form of subliminal perception during sleep was also raised.