The effects of the arousal reaction on the reduction or habituation of nystagmus in the unanesthetized cat repeatedly rotated in darkness were determined. A reduction in nystagmus was associated with a reduction of alertness as indicated by the electroencephalogram, but alerting an animal by sounds occasioned only a temporary and partial recovery of nystagmus. Further, a continuous arousal sustained by cutaneous electric shock stimuli did not prevent habituation. It is concluded that a reduction of alertness is not wholly responsible for the nystagmic reduction and that other factors, not yet identified, play a powerful role.