['To determine whether furosemide could prevent renal side effects of indomethacin (INN, indometacin) used for the pharmacologic closure of the patent ductus arteriosus (PDA) in preterm infants.', 'Thirty-six preterm infants with birth weights < 1750 gm affected by hemodynamically significant PDA were randomly assigned to one of two study groups. Group 1 consisted of 18 infants treated with three doses of indomethacin (0.20 mg/kg every 12 hours); each dose was followed by a dose of furosemide (1 mg/kg). Group 2 consisted of 18 infants treated only with the same doses of indomethacin. Body weight, urine output, glomerular filtration rate (GFR), fractional excretion of sodium (FENa+) and potassium (FEK+), and osmolal and free water clearance were evaluated in both groups before, during, and after treatment.', 'The body weight trend, serum sodium, chloride and potassium concentrations, plasmatic and urinary osmolality were similar during the treatment in both the groups. A significant reduction of urine output (p < 0.01) was detected in group 2 but not in group 1. A significant increase of blood urea nitrogen and serum creatinine was detected at the end of treatment in group 1 compared with group 2. During the treatment, a significantly higher GFR (p < 0.05) was found in group 2 than in group 1. FENa+ and FEK+ were significantly higher (p < 0.05 and p < 0.001, respectively) in group 1 than in group 2 during and after the treatment. The osmolol clearance and free water clearance were significantly higher during and after treatment (p < 0.01 and p < 0.001, respectively) in group 1 than in group 2.'] Does furosemide prevent indomethacin-induced renal side effects in preterm infants?