Twelve Lewis rats were inoculated with a guinea pig spinal cord tissue preparation. They developed experimental allergic encephalomyelitis (EAE) after 12-14 days, manifested by weight loss, tail flaccidity, ataxia, hind limb paresis and incontinence. The CNS lesions are produced in this animal model on the basis of inflammatory demyelination, which provides a useful model for multiple sclerosis. Concomitantly with EAE, all animals developed vestibular hyperreactivity (VH) of otolith and canal reflexes. In surviving animals these reflexes renormalized after full clinical recovery. The major effect on the canal response was an increased duration of postrotatory nystagmus caused by an increase in time constant. These findings are similar in part to those previously reported in patients with multiple sclerosis.