The clinical use of gentamicin (G) is limited due to its known nephrotoxic actions. Generation of reactive oxygen species has been proposed as a causative factor of cell death in the G-induced acute renal failure (ARF). Studies have indirectly shown a role for superoxide ion, by the use of superoxide dismutase (SOD) mimetics, in G-induced ARF. In this study we aimed to directly measure the enzyme activities in the in situ isolated kidneys and to investigate the effects of antioxidant therapy in preservation of endogenous antioxidant levels in this model of ARF. 35 male Sprague-Dawley rats were randomly assigned to 5 groups of control, the Tyrode perfused; G, gentamicin (200 microg/ml) added to the perfusate; G+Vit E, vitamin E (100 mg/100 g BW, im); G+Vit C, vitamin C added to the drinking water for 3 days (200 mg/l) and to the perfusate (100 mg/l); G+Vit E+Vit C, vitamins E and C were both administered. SOD activities were determined in renal tissues based on NAPDH oxidation at 340 nm by spectrophotometry. In G group, SOD activity was significantly reduced comparing to controls (p<0.05). Administration of vitamin E alone or in combination with vitamin C significantly preserved the enzyme activity levels comparing to G group (p<0.05). Antioxidant vitamins have a role on preservation of endogenous antioxidant levels, namely SOD, in G-induced nephrotoxicity.