ABSTRACT This study was designed to determine the effects of mannitol on tissue Na+/K+-ATP ase enzyme activity and malondialdehyde (MDA) levels in rabbit brain after experimental head trauma. Thirty New Zealand rabbits were divided equally into three groups: Group S(sham-operated group), group C(untreated group) and group M (mannitol treated group). Grup C and group M received head trauma with the weight drop method. Mannitol was administered 1.0 g/ kg i.v. immediately after the head trauma to group M. Head trauma was applied to the right side. One hour after trauma, brain cortices were resected from both sides and the Na+/K+-ATP ase enzyme activity and MDA levels were determined. The results were compared between S, M and C groups (p>0.05). Rectal temparature after the administration of mannitol in group M was found to be lower than groups S and C (p