Evaluation for patent ductus arteriosus by both Doppler examination and direct two-dimensional echocardiographic visualization has been reported in infants and children. However, visualization of a patent ductus arteriosus in preterm infants with lung disease has been difficult. Using a recently developed 7.5 MHz mechanical scanner with interfaced two-dimensional directed pulsed Doppler ultrasonography, 36 examinations were performed from a suprasternal approach in 27 patients (age range 1 day to 3 months, mean 18 days; weight range 490 to 2,500 g, mean 1,260). Complete imaging for evaluation of patency of the ductus arteriosus was successful in 33 (92%) of 36 examinations, and imaging of the pulmonary end of the ductus arteriosus was successful in all. In 18 examinations, the ductus arteriosus was closed by both two-dimensional echocardiography and Doppler examination. In four cases the ductus arteriosus was widely patent by both two-dimensional echocardiography and Doppler examination. Eleven echocardiographic examinations revealed a narrowed ductus arteriosus, and of these, 10 (91%) showed Doppler findings of patent ductus arteriosus. It is concluded that combined two-dimensional/Doppler echocardiographic assessment allows confident detection of both a large unrestrictive and a small, stenotic patent ductus arteriosus in preterm infants with lung disease.