Twenty-three premature infants (GA 28.8 +/- 0.5 weeks) with bronchopulmonary dysplasia (BPD) and 14 premature infants (controls, GA 33.0 +/- 1.2 weeks) with moderate respiratory distress syndrome or with mild respiratory disturbances, were evaluated for impairment of cardiopulmonary function at 50 and 120 weeks corrected age. Respiratory system compliance was reduced in both groups, but improved with advancing age. Respiratory system resistance was initially increased, especially in the BPD group, but improved gradually. Maximum flow at functional residual capacity (VmaxFRC ml/s) indicated, nevertheless, severe peripheral obstruction (flow < 84 ml/s) in 16/20 of infants with BPD and in 7/12 of control infants at 50 weeks corrected age. At 120 weeks corrected age none of the control patients had severe peripheral pulmonary obstruction (flow < 120 ml/s), while this was still found in 5/13 infants with BPD. Doppler echocardiography indicated cardiac involvement (shortened pulmonary acceleration time) in patients with the most severe peripheral pulmonary obstruction. Pulmonary morbidity was also higher in the BPD group, and these infants were shorter and weighed less than the control infants. CONCLUSION. Measurements of maximum flow at functional residual capacity as well as cardiac evaluation are essential elements in follow up of infants with severe BPD.