The purpose of the study was to determine the efficacy of furosemide in addition to intravenous fluids in the prevention of radiocontrast nephropathy. 18 patients, referred to a radiocontrast study, considered at risk because of preexisting renal insufficiency, were enrolled in a prospective, randomized, controlled trial, performed at the secondary care center of a 1,100-bed private university hospital. In addition to fluids, the treatment group received furosemide (mean dose 110 mg) intravenously 30 min prior to the injection of contrast material. The control group received fluids (mean 3 liters). Radiological studies were mostly angiographies performed with both ionic and non-ionic contrast material, at an average dose of 245 ml. Renal function significantly deteriorated in the group pretreated with furosemide (p < 0.005 by ANOVA), with a rise in serum creatinine from 145 ± 13 to 182 ± 16 μmol/l at 24 h, while no change occurred in the control group (from 141 ± 6 to 142 ± 7 μmol/l). Renal failure was associated with weight loss in the furosemide-treated group. Furosemide may be deleterious in the prevention of radiocontrast nephropathy.