OBJECTIVE--To assess relations between right ventricular pressure measured with a high fidelity transducer tipped catheter and the characteristics of tricuspid regurgitation recorded with Doppler echocardiography. DESIGN--A prospective non-randomised study of patients with severe pulmonary hypertension referred for consideration of lung transplantation. SETTING--A tertiary referral centre for cardiac and pulmonary disease, with facilities for invasive and non-invasive investigation, and assessment for heart and heart-lung transplantation. PATIENTS--10 patients with severe pulmonary hypertension being considered for lung transplantation. ENDPOINTS--Peak right ventricular, pulmonary artery, and right atrial pressures; peak positive and negative right ventricular dP/dt; peak Doppler right ventricular-right atrial pressure drop; Doppler derived peak positive and negative right ventricular dP/dt; and time intervals of Q to peak right ventricular pressure and to peak positive and negative right ventricular dP/dt. RESULTS--The mean (SD) pulmonary artery systolic pressure was 109 (29) mm Hg. The peak Doppler right ventricular-right atrial pressure drop underestimated peak right ventricular pressure by 38 (21) mm Hg, and by 21 (18) mm Hg when the Doppler value was added to the measured right atrial pressure (P values < 0.05). This discrepancy was greater for higher pulmonary artery pressures. The timing of peak right ventricular pressure differed, with the Doppler value consistently shorter (mean difference 16 ms, P < 0.05). Values of peak positive and negative right ventricular dP/dt and the time intervals Q-peak positive right ventricular dP/dt and pulmonary closure to the end of the pressure pulse differed between the two techniques in individual patients, but not in a consistent or predictable way. CONCLUSIONS--Doppler echocardiography significantly underestimates the peak right ventricular pressure and the time interval to peak right ventricular pressure in pulmonary hypertension, particularly when severe. These differences may be related to orifice geometry. Digitisation of Doppler records of tricuspid regurgitation provides useful semiquantitative estimates of absolute values and timing of peak positive and negative right ventricular dP/dt. Clinically significant differences may exist, however, and must be considered in individual patients.