The authors evaluated clinical importance of alveolar-arterial PO2 difference (AaDO2) and pulmonary artery pressure (PAP) estimated by pulsed Doppler echocardiography in 31 patients with pulmonary embolism (PE). Echocardiographic estimates from flow velocity patterns in the right ventricular outflow tract showed significant correlation with actual measurements obtained by right cardiac catheterization. Furthermore, PAP as obtained by pulsed echocardiography was significantly higher in acute massive and recurrent multiple groups in comparison with the acute submassive group. AaDO2 was greatest in the acute massive group, followed by the recurrent multiple group, and then by the acute submassive group. These results suggest that analyses of AaDO2 and the echocardiographic estimation of PAP at bedside are successful in the diagnosis and classification of PE.