We conducted a prospective study to examine the effect of pentobarbital administration on the development of seizures in dogs that had undergone cervical myelography with metrizamide while anesthetized with halothane. Thirty dogs scheduled for cervical myelography were assigned to 3 groups. Dogs in group 1 received no pentobarbital. Those in group 2 were administered pentobarbital (5 mg/kg, IM) before induction of anesthesia, and those in group 3 received pentobarbital at the end of the procedure when the anesthetic vaporizer was turned off. Anesthesia was induced with thiamylal sodium in all dogs and was maintained with halothane. Dogs that underwent surgery immediately after the myelography were not included in the study. A significant difference was not found among the 3 groups in terms of number of dogs that had seizures, mean body weight of the dogs, duration of anesthesia after injection of metrizamide, time from extubation to first seizure, volume of metrizamide injected, or clinician performing the myelography.