A method for quantification of regurgitant volume in mitral regurgitation (MR) was studied. 31 cases of MR were investigated with color Doppler. The reliability of measuring velocity by Doppler and the influence of pressure gradient on MR were assessed and confirmed by experimental device. The results suggested that the best method in quantification of the regurgitant volume was "calibrating method" (r = 0.99; P less than 0.01), the next to the best was "volume method" (r = 0.74; P less than 0.01), whereas the regurgitant volume evaluated by multiplication of area, velocity and time was far from the actual regurgitant volume (r = 0.47; P greater than 0.05). The velocity of blood flow measured by Doppler is closely correlated to results obtained from experiments (r = 0.69; P less than 0.05). We believe that the ratio of back flow area and average area of left atrium calculated by Helmcke's method reflects the severity of the disease to a certain degree, bu there are many problems unsolved, e.g. the determination of the velocity of blood flow by color Doppler is dependent on the degree of brightness of coloration; the brighter the color, the quicker the speed it represents, whereas the darker coloration speaks for slower speed.