The present study was undertaken to evaluate a new non-invasive approach to the quantification of mitral regurgitation. Doppler echocardiography and left ventriculography were performed in 20 patients without valvular heart disease (group A), and in 30 patients with pure mitral regurgitation (group B). Volumetric flows through the aortic and mitral valve orifices were determined by Doppler technique. The aortic flow (AF) was calculated as the product of the aortic orifice area by the systolic velocity integral. The mitral flow (MF) was computed as the product of the corrected mitral orifice area by the diastolic velocity integral. The mitral regurgitant fraction (RF) was calculated as: RF = 1 - AF/MF. In group A, there was a close agreement between aortic and mitral flows (r = 0.94, P less than 0.001), and there was no significant difference between the two measurements. In group B, the mitral flow was significantly higher than the aortic flow. The regurgitant fraction assessed by Doppler echocardiography correlated well with the grades of severity of regurgitation obtained at left ventriculography. We conclude that combined measurement of both aortic and mitral flows by Doppler echocardiography provides a new and promising approach to the noninvasive quantification of mitral regurgitation.