In experiments using rabbits, the pupil on the side of irritative inner ear lesion showed dilatation, and that on the side of paretic lesion showed constriction. In the clinical observation of patients with unilateral inner ear diseases (134 cases), anisocoria was recognized in 54.5%. In 68.5% of these, anisocoria was induced after applying a drop of neosynephrine. The size of the pupil on the affected side was smaller in 65.8% than the pupil on the healthy side. Anisocoria in inner ear lesions is believed to be due to vestibulo-sympathetic imbalance through the superior cervical sympathetic ganglion.