The existence of a threshold for the production of fast components of vestibular nystagmus was investigated in the rabbit. The characteristics (position and velocity) of reflexive eye movements were precisely monitored with the use of the search-coil method and a laboratory computer. The threshold largely depended on the eye position in the orbit during nystagmus and, to a much lesser extent, on the eye velocity. The basic characteristics of the threshold remained unchanged under vestibular stimulation in the dark and in the light, and for different frequencies and peak velocities of rotation. A pattern of vestibular nystagmus was demonstrated whereby it is possible to predict the occurrence of fast components.