Spinal cord ischemia was produced in rabbits by temporary occlusion of the abdominal aorta just distal to the renal arteries; and recovery, or failure to recover, was assessed by examining the rabbits for permanent loss of sensory and motor function in the hind limbs. A temperature reduction of 3 degrees C during the period of circulatory impairment caused a doubling of the duration of ischemia that could be reversibly sustained. Intravenous administration of 5 mmoles/kg of MgCl2 before the ischemia (a dose sufficient to produce neuromuscular blockade) caused a 50% increase in the tolerable duration. The combination of the 3 degrees C reduction in temperature and the elevated Mg++ increased by about 3 fold the duration of ischemia that could be sustained before irreversible damage occurred. These results may have implications for the care of patients subjected to marginal degrees of CNS ischemia.