Contrast nephropathy (CN) remains a common cause of acute renalfailure in patients undergoing radiocontrast studyIt is the third leading cause of hospital-acquired acute renalfailure (ARF) after hypotension and surgery.The present study including thirty diabetic patients,who were subjectedto coronary angiography from whom 20 patients were treated with N.acetylcystein (NAC) and 10 patients received placebo beforeangiography, all patients were classified into 2 groups:1. NAC group: 20 patients who received NAC 600 mg/8 hourssdiluted in 100 cc of water and intravenous saline 0.45% at arate 1 mL/Kg/hour 24 hours before coronary angiographyand for 48 hours after angiography.2. Control group are 10 patients who received intravenoussaline 0.45% at a rate 1 mL/Kg/hour 24 hours beforecoronary angiography and 48 hours after coronaryangiography.Serum creatinine, creatinine clearance, urinary Nitric oxideproduct (NOx) and urinary MDA were measured before , 24 hours and96 hours after coronary angiography.