Objectives - This study was designed to determine whether acetylcysteine could provide a protective effect on renal function in a population of patients with normal renal function or mild to moderate chronic renal failure, usually referred for a coronary procedure. Background - Contrast-induced nephropathy is a well-recognized complication of coronary angiography. Recent studies suggest that saline hydration and acetylcysteine reduce the incidence of contrast-induced worsening of renal function in patients with pre-existing chronic renal failure who are undergoing computed tomography examinations. Methods - One hundred eight patients were blindly and randomly assigned to receive either acetylcysteine or placebo before and after administration of contrast agent in association with a moderate hydration protocol. Serum creatinine and urea nitrogen were measured before and 24 hours after coronary procedure. Results - The mean serum creatinine concentration remained unchanged 24 hours after contrast agent administration in both groups: from 1.04 ± 0.26 to 1.03 ± 0.29 mg/dl in the acetylcysteine group and from 1.16 ± 1.1 to 1.06 ± 0.41 mg/dl in the control group (p = 0.29, for the comparison between two groups, NS). We divided the population into 3 subgroups according to their creatinine clearance: no significant change of serum creatinine concentration was observed in patients with normal renal function nor in patients with pre-existing mild to moderate chronic renal failure in both groups. There was no significant difference for the incidence of contrast-induced nephropathy between both groups (2 of the 53 patients in the acetylcysteine group and 3 of the 51 patients in the placebo group, p = 0.98, NS). Conclusions - Our data do not support the systematic use of acetylcysteine before a coronary procedure in patients with normal renal function or mild to moderate chronic renal failure, to prevent contrast-induced nephropathy.