Five horses, weighing 337 to 400 kg, were used in this research, one of them being used as control. Cervical myelography with iohexol (Omnipaque) was performed on four horses tranquilized with flunitrazepan before induction of anesthesia with sodium thiopental. Anesthesia was maintained with fluothane and oxygen. Cerebrospinal fluid (CSF) was analysed before and after an injection of ioxheol into the subarachnoid space. The animals received 25 to 50 ml of iohexol, after removal of 20 ml cerebrospinal fluid. Radiographies were taken with the horses at lateral recumbency, and the cranial, central and caudal regions of the cervical spine being focalized. No significant changes occurred in the cerebrospinal fluid after injecting the contrast medium. Pathologic changes were not found by gross or microscopic examination of the brain and the cervical spinal cord. Radiographies of good to excellent image quality were obtained. At autopsy, radiographic diagnosis of cervical vertebral instability was confirmed in the animal that had pelvic limb ataxia.