Aims To determine laboratory and clinical benefit of oral acetylcysteine, as an adjunct to saline hydration, in chronic renal insufficiency patients undergoing coronary angiography. Methods and results We prospectively studied 80 patients with chronic renal insufficiency (mean [+/-SD] serum creatinine concentration 2.0+/-0.39 mg/dl), who underwent coronary angiography with or without intervention. Patients were randomly assigned to receive either acetylcysteine (600 mg orally t.i.d.) or placebo, in addition to intravenous 0.45% saline (1 ml/kg of body weight per hour), 12 h prior to and after coronary angiography. There was an increase of 20.5 mg/dl in the serum creatinine concentration 48 h after coronary angiography in seven of the 80 patients (9%): in four of the 41 patients (10%) in the acetylcysteine group and in three of the 39 patients (8%) in the placebo group (P=0.52). The incidence of in-hospital adverse clinical events (acetylcysteine, 5% vs placebo, 8%, P=0.47) and the length of hospital stay [acetylcysteine, median (interquartite range) 4 (2-4) days vs placebo, 2 (2-4) days, P=0.44] did not differ significantly between the two treatment groups. Conclusion Our findings do not support routine prophylactic administration of oral acetylcysteine as an adjunct to saline hydration for the prevention of contrast-induced nephropathy in chronic renal insufficiency patients undergoing coronary angiography. (C) 2003 The European Society of Cardiology. Published by Elsevier Ltd. All rights reserved.