The alteration of renal function after initiation of mannitol infusion were monitored in 20 patients with cerebrovascular accident to evaluate whether mannitol has nephrotoxicity effects. Serum creatinine and urea nitrogen were increased after initiation of mannitol infusion, but hadn't reached stagistical significance. Urinary and serum alpha 1-microglobulin, beta 2-microglobulin and urinary NAG, gamma-GT were significantly increased after 5-10 days successive infusion of mannitol (P < 0.05). The results suggest that the acute nephrotoxicity effect of mannitol should not be ignored.