Twelve subjects were studied for a total of 30 nights of uninterrupted sleep by simultaneous recording of EEG, eye movements, heart rate, respiration, and systolic blood pressure. In agreement with previous reports, progressive decreases in heart and respiratory rates and an early fall followed by a sustained rise in systolic blood pressure were found to be consistent base-line trends. Superimposed upon these trends and coinciding with the regular recurrence of stage I rapid eye movements (REM) there were periodic changes in these three functions of two kinds: a) slight increases in average level and b) marked increases in minute-to-minute variability. The changes in average level of blood pressure and of both blood pressure and heart rate variability were more conspicuous during the later REM periods of the night. Alternative interpretations and possible medical implications of these findings are discussed. dreaming; sleep and EEG; eye movements and sleep Submitted on October 11, 1963