Purpose : B-Type Natriuretic Peptide (BNP) has a major role in screening and diagnosis of cardiac disease and monitoring of the treatment response in children and adults. Plasma BNP measurement has been reported to be a benefits in the diagnosis of hemodynamically significant PDA in neonates. The aim of our study was to investigate the usefulness of a BNP assay as a biochemical marker for the diagnosis of symptomatic PDA(sPDA) in preterm infants. Methods : Preterm Infants born at <37 weeks��� gestational age were prospectively enrolled within 24 hours of birth. Plasma BNP levels were measured on days 1, 4, and 7. BNP concentrations were detected using a commercial diagnositics (Abbott diagnostics, AxSYM). Significant PDA was diagnosed by large ductal flow with left to right shunt on color Doppler echocardiography, along with clinical features of PDA. And then sPDA was treated with indomethacin. Results : 19 preterm infants were prospectively enrolled into the study. Seven infants with PDA had higher day 4 plasma BNP values (median 2164 pg/ml; range 644~4000) than control group (median 98 pg/ml; range 39~167). The area under the receiver operator characteristic curve for the detection of sPDA was high : 0.982 (95% confidence interval; 0.947~1.018). The cutoff of BNP concentration for the diagnosis of sPDA was determined to be 610 pg/mL (sensitivity: 100%; speciticity : 95%). Conclusion : BNP may be a useful screening tool for the presence of a PDA in premature neonates as levels of BNP are high in the presence of a significantly patent duct. Serial BNP measurements may be of value in assessing the clinical course of PDA. Key Words : Preterm infants , B-Type Natriuretic Peptide, Patent Ductus Arteriosus, color Doppler echocardiography