The effect of direct antigen (KLH) challenge of endolymphatic sac (e. sac) on caloric response was investigated in guinea pigs. The caloric response was not significantly suppressed both in the primary KLH challenged ears and in the PBS challenged ears as compared to the unchallenged contralateral ears. In the animal of secondary KLH challenge of the e. sac, the caloric response was significantly reduced in the challenged ears as compared to the unchallenged contralateral ears and to the PBS challenged ears. These result suggested that local immune reaction mounted in the e. sac caused immune injury not only to the e. sac but also to the vestibular function.