The systemic vascular response to seizures in known but information on the hemodynamics of the pulmonary circulation is lacking, clouding an understanding of the pathophysiology of postical pulmonary edema. We investigated this problem using electrically induced single seizures and bicuculline-induced status epilecticus in halothaneanesthetized sheep. Aortic, pulmonary arterial, and left atrial pressures were recorded throughout the seizure activity, and the responses of the systemic and pulmonary pressures were compared. All monitored pressures rose precipitously with the onset of seizures. In all types of seizure the pulmonary pressure elevation was brief, lasting only one-third as long as did the systemic. Pulmonary microvascular pressures rose well above the level of plasma oncotic pressure. Pulmonary vascular pressures were elevated in proportion to the duration of the seizure stimulus, while the systemic response did not so vary. Cervical spinal cord transection abolished all systemic and pulmonary vascular response to seizures, demonstrating ultimate neural mediation.