Retrograde cerebral perfusion has been a useful technique for preventing brain damage during hypothermic circulatory arrest. To determine the optimum conditions for retrograde cerebral perfusion utilizing a fluorescence vital microscope, male Wistar rats weighing 100 to 300g were used for infusing saline with contrast medium (0.01% FITC-albumin) through the external jugular vein. A closed cranial window was prepared over the pial surface of the brain at the medial part of the right parietal cortex in order to observe the blood flow of tributaries from the middle cerebral artery to the superior cerebral vein. Intracranial pressure was controlled at 3±2cmH₂O for comfortable visualization. The observation of retrograde cerebral perfusion was performed under hypothermic conditions. Cerebral blood flow could not be observed under retrograde pressure of 5-15mmHg, mainly due to venovenous shunt flow. But retrograde cerebral perfusion was observed with a driving pressure of 15-30mmHg, and flow velocity measured by the video tracing method (n=5) in arterioles (mean diameter 37±10μm) was -12±5μm/sec, in venules (mean diameter 64±17μm) was -14±9μm/sec, which was 405±92μm/sec and 220±150μm/ sec under hypothermic beating heart conditions respectively. Under retrograde pressure of 30-50mmHg, cerebral microcirculation was deteriorated with increasing cerebral volume, and cerebral blood flow was consequently interrupted. In conclusion, the optimal condition for retrograde cerebral perfusion was determined under retrograde perfusion pressure of 15-30mmHg and intracranial pressure of 3±2cmH₂O, whenever cerebral microcirculation from venule to arterioles was best. Retrograde cerebral perfusion has some advantage for cerebral protection compared with hypothermic circulatory arrest, but might not supply sufficient cerebral blood flow to prevent brain damage.