A transducer tipped catheter and simple recording system were used for the continuous measurement of ambulatory pulmonary artery pressure. The pulmonary artery pressure was recorded on a miniaturised tape recorder and replayed via an optical writer. Pulmonary arterial systolic and diastolic pressures can be analysed on a beat to beat basis. Continuous ambulatory monitoring was performed for a total 288 hours in 13 patients who were undergoing routine investigation for coronary artery disease. There was less than 1% zero drift and 0.25% linearity error per full scale pressure. The frequency response of the entire system was flat to 8 Hz with a linear phase delay. The transducer tipped catheter and a conventional fluid-filled system were used to measure left ventricular and pulmonary artery end diastolic pressures in eight patients. The correlation between the results obtained by the two methods was excellent. This method could be used at any centre equipped for ambulatory electrocardiographic monitoring.