[Bilateral vestibular areflexia: quantification is required].

Bilateral vestibular loss, that should be more precisely qualified as "horizontal semicircular canal bilateral loss", is a concept usually defined by the following characteristics: - no response to caloric tests, - no response to pendular test with a 20-second period, - increasing gain of the cervico-ocular reflex. We present five cases. We increased the stimulation frequency to a level higher than usually, employed and observed that: - at a given frequency threshold a certain amount of reactivity may be observed, - above that threshold the reactivity increases in proportion with stimulation frequency. The apparent vestibular loss is actually related to stimulation frequency. This phenomenon could be explained by considering the physiology of phasic and tonic cells.