To determine if furosemide would prevent the renal side effects of indomethacin therapy in premature infants with patent ductus arteriosus, 19 premature infants were randomized into two groups: nine received indomethacin alone, and ten received indomethacin followed immediately by furosemide. There was no significant difference between the groups in birth weight, gestational age, postnatal age, and in cardiopulmonary or renal status at the time of study. Infants who received indomethacin and furosemide had significantly higher urine output (P less than 0.05), higher FENa and FECl (P less than 0.01), and higher glomerular filtration rate (P less than 0.05) than those of infants who received indomethacin alone. Seven infants in each group responded to indomethacin therapy with disappearance of PDA murmur and improvement of cardiovascular status. The results of this study suggest that furosemide may prevent the renal side effects of indomethacin therapy and yet not affect the efficacy of indomethacin in the closure of a PDA.