AIM: To investigate the effects and mechanisms of irbesartan,one of the angiotensin Ⅱreceptor blockers,on kidney function in diabetic rats. METHODS: Forty adult male Wistar rats were randomly divided into four groups: control group,diabetes group,irbesartan group and captopril group. At the end of 12 weeks,the rats were sacrificed. Urine volume,body weight,kidney weight/body weight,plasma,glucose,glycosylated hemoglobin (HbA_1c),urinary ?_2-microglobulin (?_2-MG) excretion,urinary albumin excretion rate (UAR),creatinine clearance (Ccr) were measured. Nitric oxide (NO) and endothelin-1 (ET-1) levels in plasma,urinary and renal tissues were determined. RESULTS: Urine volume,kidney weight/body weight,plasma glucose,HbA1C,UAR,Ccr,urinary ?_2-MG excretion,NO and ET-1 levels of urinary,blood and renal tissue in diabetic rats were significantly higher than those of normal controls ( P