We evaluate the prevalence of deterioration of renal function among patients undergoing coronary angiography with or without PCI and role of N-Acetylcysteine in renal protection .one hundred and eighty –three patients were enrolled in the study. One hundred and two patients had a normal serum creatinine and were taken as a control group. The remainder 81 patients had a serum creatinine of <1.4 mg/dl and were divided into 2 groups: group 1: received N-Acetylcysteine and isotonic saline hydration and group 2 received isotonic saline hydratation and placebo.