In this study a total of 19 rabbits, divided into five groups were used to evaluate the effects of ionic and non-ionic contrast agents on kidneys which were unilaterally obstructed. Complete ureteral ligation was performed on the rabbits in groups I, IV and V, and contrast medium in the'amount of 1 mg/kg per week was injected to the rabbits in groups II, III, IV, and V. At the end of the fourth week nephrectomy specimens were examined histopathologically. Similar pathological findings (tubular dilatation, proteinaceous material accumulation in tubulus lumen, flattening of papillae in the medulla and necrotic changes in the papillae facing renal pelvis) were determined in obstructed kidneys with both ionic and non-ionic contrast medium. But, in non-obstructed kidneys, proteinaceous material accumulation was more evident with ionic contrast medium. Non-ionic contrast medium produced less microscopic damage on the kidneys.