We tested the hypothesis that prolonged maintenance indomethacin therapy would allow more effective closure of patent ductus arteriosus (PDA) and thereby decrease the recurrence rate. Thirty-nine low birthweight neonates (less than 1500 gm) with confirmed PDA were randomly assigned in a double-blind fashion to receive standard indomethacin therapy (three doses), followed either by maintenance indomethacin therapy (0.2 mg/kg/day) for 5 days or by an equivalent volume of placebo for 5 days. Of the 20 infants who received maintenance indomethacin therapy, two (10%) required additional therapy and one of these required surgical ligation. Of the 19 infants who received only the first three indomethacin doses, nine (47%) required additional therapy for PDA (p less than 0.05) and seven of these had a ligation (p less than 0.05). We conclude that maintenance indomethacin therapy, in comparison with short-term indomethacin therapy, decreases the incidence of surgical PDA ligations, eliminates most PDA recurrences, and does not increase toxic effects of indomethacin in the low birth weight infant with PDA.