The effects of lower extremity hypothermia during aortic cross-clamping are unknown. To compare the effects of lower extremity hypothermia with normothermia during aortic cross-clamping, two groups of six (25-40 kg) anesthetized pigs had their aortas cross-clamped below the renal arteries for 2 h. The cold group had their lower extremities cooled during cross-clamping to a quadriceps muscle temperature of 28°C by using convective cooling. The warm group had the quadriceps muscle temperature maintained at 38°C with convective warming. Saline, 0.9%, was used to maintain the pulmonary capillary wedge pressures at 5 mm Hg in both groups. Reperfusion of the lower extremities resulted in a small but significant decrease in the blood temperature from 36.6 ± 0.3°C (mean ± SE) to 35.6 ± 0.3°C 1 min after reperfusion in the cold group, but did not change the blood temperature in the warm group. Both the cardiac output and the lower extremity arterial flow were greater in the cold group at 1 and 5 min after cross-clamp release. Also one pig in the warm group required resuscitation with 1 mg of epinephrine intravenously to treat severe hypotension and myocardial depression after cross-clamp release. We conclude that hypothermia of the lower extremities may be beneficial for surgery involving aortic cross-clamping.