To investigate whether the development of symptomatic patent ductus arteriosus could be predicted, 26 preterm infants dependent on mechanical ventilation were examined daily with Doppler and M-mode echocardiography until 3 days after birth. The presence or absence of a hemodynamically significant ductus shunt, as judged from echocardiographic criteria, was tested for predictive power in terms of sensitivity, specificity and total error rate. Out of the 26 infants 13 developed symptomatic patent ductus arteriosus at a median age of 5 days (range 2-8). These 13 infants developed echocardiographic evidence of a large shunt at a median age of 2 days (range 1-3). The sensitivity of prediction was 18, 46 and 100% at 1, 2 and 3 days after birth. The specificity was 80, 92 and 85% and the total error rate was 52, 32 and 8%. Thus, accurate prediction was possible 3 days after birth.