We investigated the effect of urinary alkalinization accomplished by intraperitoneal injection of sodium bicarbonate and acetazolamide on gentamicin nephrotoxicity in male Fisher 344rats. Forty rats (body weight 200-300g) were divided into four groups: control (gentamicin 20mg/kg, bid), high sodium load (gentamicin 20mg/kg, 25cc of saline, bid), low bicarbonate (gentamicin 20mg/kg, 25cc of sodium bicarbonate 100mEq/L, 2.5mg of Diamox, bid) and high bicarbonate (gentamicin 20mg/kg, 10cc of sodium bicarbonate 250mEq/L, 2.5mg of Diamox, bid) groups. All drugs and electrolyte solutions as mentioned above were administered intraperitoneally twice a day for seven days and changes in renal functions were studied. While salt loading failed to influence the severity of gentamicin nephrotoxicity, urinary alkalinization induced by bicarbonate and acetazolamide injection showed remarkable ameliorating effects on gentamicin nephrotoxicity. The high bicarbonate group exhibited more beneficial effects than the low bicarbonate group on gentamicin nephrotoxicity. So, urinary alkalinization seems to be an effective method for the prevention of gentamicin nephrotoxicity in rats.