Trial A was a randomized, double-blind trial in which indomethacin plus usual medical therapy was compared with a placebo plus medical therapy. Where this regimen was unsuccessful, the code was broken, and infants who received indomethacin were treated surgically. Infants who had received placebo in Trial A were entered, if there were no contraindications to indomethacin, into Trial B. In Trial B, infants were randomized to surgery or indomethacin therapy. Those in whom indomethacin treatment was unsuccessful were treated surgically. The Recruitment and Intervention Phase began in April 1979. All patients were enrolled by March 31, 1981, and followed for one year after enrollment.