The vestibulo-ocular response (VOR) was recorded during natural sleep in cats with chronically implanted electrodes. By using a small amplitude sinusoidal head rotation (11 degrees) peak-to-peak at 0.4 Hz) which elicited only slow compensatory eye movements, the VOR amplitude was found to decrease steeply (down to 40% or less) during slow-wave sleep. The phase of the VOR with respect to head position remained approximately constant. With a larger amplitude of sinusoidal rotation (320 degrees peak-to-peak at 0.05 Hz) the VOR response included nystagmus. During slow-wave sleep, nystagmus disappeared and the overall amplitude of the response decreased. Simultaneously, the phase of the eye response with respect to head position shifted by up to 90 degrees in advance. During paradoxical sleep, VOR disappeared in all cases and was replaced by randomly occurring bursts of rapid eye movements. These results are discussed in terms of a parametric control model of VOR.