In replantation and tissue transplantation an ischemic period is inevitable until blood flow is reestablished. This study evaluated the reflow patterns of the rat cremaster microcirculation after warm and cold ischemia with the use of vital microscopy. The present studies indicate that hypothermia (cold temperatures of about 5 degrees C) protects arteries from excessive spasm during ischemia and also lessens the reactive hyperemia. The enhanced reflow patterns may be attributed to decreased vessel injury and the diminution of metabolic needs of the hypothermic muscle. These results support the use of hypothermia even for short ischemic periods during microsurgery procedures in order to prevent adverse effects on the reflow patterns of the tissue.