During the past year, we have monitored continuous pulmonary artery pressure in 9 critically ill newborns (weight range 2.2 to 4.4 kg and gestational age 36 to 43 weeks) with persistent pulmonary hypertension (PPAR). Indications for monitoring were 12 to 24 hours of PaO2 <60 on 100% inspired oxygen and suprasystemic pulmonary hypertension at cardiac catheterization. Cardiac catheterization data on these patients showed right to left shunting at the foramen ovale and/or ductal level with pulmonary artery pressure (PAP) greater than systemic arterial pressure (SAP) by a mean of 21.0 mm Hg (P<0.05). NIH #5 catheters placed by saphenous vein cutdown remained in position after fluoroscopic confirmation of location. SAP was obtained from indwelling umbilical or radial arterial catheters. SAP and PAP were displayed at bedside on digital readouts and continuously recorded on a computerized trend recording. Catheters remained in place for a range of 24 to 336 hours (mean 112 hours) and were removed after PaO2 >50 mm Hg on 60% inspired oxygen. Eight patients survived and two patients had local infections at the cutdown site. PAP levels permitted regulation of specific therapy for pulmonary hypertension (correction of pH and intrapulmonary artery tolazoline in 7/ 9). In critical situations where PPAH is the principle cause of severe hypoxemia in neonates, this selective approach for documentation of response to therapy is warranted.