Mefenemic acid (MA) was given in three doses of 2 mg/kg/dose at 12 hourly intervals in 16 cases clinically suspected of having symptomatic patent ductus arteriosus (PDA). All babies were 35 weeks gestation (mean 30.1 weeks) and weighed less than or equal to 1700 g at birth (mean 1320 g), the mean age of administration of MA being 16 days. Of the 16 cases, two did not respond to therapy. One non-responder was subsequently shown to have an endocardial cushion defect without PDA on 2-D Echo and Doppler study. The other was 29 days old at the initiation of therapy. In once case, the ductus reopened after an initial closure, however, it closed on repeating a second course of the drug. Thirty preterms (less than or equal to 34 weeks) who were earlier treated with three doses of indomethacin (0.25 mg/kg/dose) formed the comparative study group. The closure rate of PDA on treatment with indomethacin was 70% and that with MA was 93.3% (p greater than 0.05). Two neonates treated with MA and two treated with indomethacin had feeding intolerance and vomiting, perhaps attributable to the drug therapy. We recommend the use of MA for closure of symptomatic PDA in preterms, especially in those cases where indomethacin is not tolerated or when minute titration of its dosage is impracticable.