D-Mannitol, a natural product isolated and purified from the herbs of Peucedanum harry-smithii var. subglabrum, increases the osmotic pressure and urine volume as a protective agent on renal tubules. Mannitol infusion performed immediately after restitution of blood flow following temporary cerebral ischemia remarkably reduced the size of the cerebral cortical focal infarction by decreasing the swelling of the end-feet, thus preventing the microvascular compression and stasis and thereby microvasculogenic secondary focal cerebral ischemia.