This study examined the effects of 1°C hypo- or hyperthermia on in vivo liver ischemia and reperfusion (I/R) injury in 15 fasted male Wistar rats. Rats were ventilated, and rectal temperature was maintained at 36, 37 (normothermic), or 38°C. In all rats, 70% liver ischemia was induced by clamping the afferent vessels to the median and left lateral lobes for 60 min, and reperfusion was allowed for 90 min. Changes in plasma aspartate aminotransferase (AST), alanine aminotransferase (ALT), and -glutathione S-transferase (-GST) levels were measured, hemodynamics and bile secretion were monitored, and arterial blood-gas analysis was performed. All ventilated rats showed a normal pH, arterial PCO₂, and arterial PO₂. AST, ALT, and -GST levels were significantly higher in the 38°C group when compared with the 36 and 37°C groups after ischemia. No differences in bile secretion were found between all groups. Histopathological alterations were in agreement with AST, ALT, and -GST levels in plasma. We conclude that a decrease of only 1°C in body temperature significantly attenuates liver I/R injury, whereas an increase of 1°C significantly increases liver I/R injury.