In order to noninvasively estimate pulmonary arterial pressure, we examined the clinical validity of a color-pulsed Doppler echocardiography in 17 patients with chronic respiratory disease. We, then compared them with the findings from a right-heart catheterization. The parameters obtained by the color-pulsed Doppler echocardiography included the pre-ejection period (PEP), the acceleration time (AT) and the ejection time (ET). The mean pulmonary arterial pressure obtained by a right-heart catheterization showed a high correlation with the PEP/AT (r=0.92). Although the M-mode echocardiography supplied only qualitative information of the pulmonary arterial pressure, the pulmonary arterial flow spectral analysis by the color-pulsed Doppler echocardiography permitted a quantitative estimate of pulmonary arterial pressure in patients with chronic respiratory diseases. Aeration of the lung sometimes obstructs right-heart visualization (information about the right heart was inadequate in 15 out of 46 cases in a previous M-mode echocardiographic study); however, once we obtained a pulmonary arterial flow pattern as a color image, we could reliably estimate the pulmonary arterial pressure for the above flow parameters (pulmonary arterial flow pattern could not be determined in only 5 of 46 similar cases). We, therefore, conclude that the PEP/AT is a useful parameter for estimating the pulmonary arterial pressure, and that the detectability of the pulmonary arterial Doppler signal by a color-pulsed Doppler echocardiography is better than that of the pulmonary arterial valves or right ventricular wall through a M-mode echocardiography in patients with chronic respiratory diseases.