Several protective measures have been described to prevent contrast-induced nephropathy (CIN). This study is aimed to evaluate the effect of a high dose of N-acetylcysteine (NAC) plus hydration, a low dose of NAC plus ascorbic acid and hydration or hydration alone on the prevention of CIN in high-risk patients undergoing elective coronary artery intervention. We conducted a randomized, prospective, placebo-controlled trial of 105 high-risk patients undergoing elective cardiac catheterization. The patients were divided into three different groups: Group A (n=30), NAC 1200 mg orally before angiography and 1200 mg orally twice daily for three doses along with good hydration; Group B (n=30), NAC 600 mg before angiography and 600 mg orally twice daily for three doses plus ascorbic acid (3000 mg one dose) before angiography and 2000 mg two doses after angiography and good hydration; and Group C (n=45), hydration with 0.9% saline started just before contrast media injection and continued for 12 h at a rate 1.0 mL/kg//min after angiography or 0.5 mL/kg/h in cases with overt heart failure for 12 h. CIN was defined as an increase in serum creatinine of >25% of baseline or an absolute increase of 0.5 mg/dL above baseline after 48 h. The incidence of CIN was significantly lower in Group A (6.66%) compared with Group B (16.66%) or Group C (17.77%). The difference between Groups A and B and between Groups A and C was also highly significant (P=0.001). In contrast, the difference between Groups B and C was not statistically significant (P=0.37). Our study indicates that high doses of NAC plus hydration provide better protection against CIN than combination therapy of NAC and ascorbic acid plus hydration, or hydration alone.