Objective To study whether mannitol renal injury can be prevented by administering small dose dopamine without withdrawing mannitol.Methods Thirty adult rabbits were divided into three groups at random: control group(normal saline,NS),non-prevented group [20% mannitol 2g/kg+NS 4.6g/(kg?min),twice a day];prevented group(20% mannitol 2g/kg+dopamine 4.6g/kg min,twice a day).The changes of Bun,Cr,Na+ and K+ were observed.After the experiment the nephridial tissues were made into histological sections,the pathological changes were observed through microscope.Results The contents of Bun and Cr in blood of the non-prevented group were obviously elevated since day 8 and the difference was significant compared to the control group;the contents of Bun and Cr in the prevented group exceeded significantly those in the control group since day 9 between the non-prevented group and the prevented group.There was no significant difference before day 10.Since day 10,the difference became significant.No abnormality was found in the histological section of the control group.Both the renal tubular epithelial cells of the prevented group and non-prevented group were swollen and the renal tubular luminas were confined;however,the pathological changes in the non-prevented group were more severe than those in the prevented group.Conclusion It is effective to administer small-dose dopamine early to protect renal function.