A study was made of vestibular stability in man as affected by acceleration in various directions and of acceleration affecting receptors of the vestibular apparatus with varying frequency. It was established that tolerance for vestibular stimulation in certain individuals may be affected by direction of acceleration and frequency of the action. Individual susceptibility to motion sickness is widely expressed under conditions of specific vestibular stimulation. The results obtained indicate that development of motion sickness does not depend on the activity of the vestibular analyzer and motion sickness is not its specific vestibular reaction. Motion sickness is a reaction of the whole organism and its manifestation under long stimulation of receptors of the vestibular apparatus in individuals predisposed to motion sickness depends on specific features of the activity of the limbico-reticular complex.