We wish to study the efficacy of N-acetylcysteine as an agent to prevent radiocontrast nephropathy in ED patients undergoing computerized tomography. We propose a randomized, double-blind, controlled trial comparing saline hydration plus N-acetylcysteine versus saline hydration alone. The hypothesis of this study is that N-acetylcysteine with normal saline will be more effective than saline alone in the prevention of radiocontrast nephropathy.