Adult mongrel dogs (29) were subjected to profound hypothermia and 90 min of total circulatory arrest. Pure surface (group 1) hypothermia and combined surface/perfusion techniques with bubble (group 2) and membrane (group 3) oxygenator systems were employed. Circulation was arrested at average esophageal temperatures of 18.4, 11.9 and 8.5.degree. C in groups 1, 2 and 3, respectively. Three animals in group 1 failed to resuscitate. All survivors in the pure surface series developed postoperative gait (hypermetria) disturbances. One intraoperative death occurred in group 2 and 4 of 8 dogs arrested at esophageal temperatures > 10.degree. C but < 15.degree. C developed motor disturbances during a 3 wk neurologic evaluation period. Animals arrested below 10.degree. C (esophageal) did not display postoperative neurological abnormalities. Three dogs in group 3 died from a hemorrhagic diathesis of uncertain etiology. None of the survivors (5) that were cooled and arrested below esophageal temperatures of 10.degree. C developed motor or sensory disturbances. Apparently, in the canine model, the CNS can be protected for 90 min of total circulatory arrest at esophageal temperatures < 10.degree. C.