To assess the diagnostic significance of color Doppler and two-dimensional echocardiography and signs in aortic regurgitation (AR), we studied 48 patients with AR confirmed by color Doppler. On color Doppler, an abnormal diastolic flow originating from the aortic valve was visualized in the left ventricular outflow tract in the 48 cases. The maximal regurgitant jet area was 0.8-23.3 cm2. On two-dimensional echocardiography, the appearance of cardiac chamber and valves did not offer a clue to the existence of AR in 12 patients (25%). On physical examination, diastolic murmur was inaudible in 18 of 45 patients. Peripheral signs of AR were not found in 20 of 45 patients. In slight AR, signs were usually not detected. From the above we are led to conclude that of the patients with AR confirmed by color Doppler echocardiography, only 75% could be detected by two-dimensional echocardiography and about 55% diagnosed by physical examination.