To evaluate the relationship between the motion pattern and degree of organic change of the anterior mitral leaflet (AML) and the features of the mitral component of the first heart sound (M1) or the opening snap (OS), 37 patients with mitral stenosis (MS) were studied by auscultation, phonocardiography and echocardiography. Based on the features of M1 and OS according to auscultation and phonocardiography, the patients were categorized as group I, 18 patients with loud and snappy M1 and OS; group II, 12 patients with snappy M1 but small and dull OS; and group III, seven patients with small and dull M1 and OS. Intensities of M1 and OS were calculated by the ratios of their amplitudes to the aortic component of the second heart sound on the high frequency phonocardiograms recorded at points of the maximum intensities, respectively. Echocardiographic parameters related to productions of M1 and OS were obtained from M-mode and two-dimensional echograms of the AML; they were amplitudes and velocities on closing and opening, M1 area defined as that between end-diastolic and systolic echoes, OS area between systolic and early diastolic echoes, the doming area between the trailing edge of an early diastolic echo and a line projected from the anterior annulus to the tip of the leaflet, and the degree of systolic ballooning. Results were as follows: 1. Significant differences in the area of the mitral valve orifice were found among three groups. The area was maximum in group II, minimum in group III and intermediate in group I. 2. In group I, the body of the AML was pliable, resulting in a ballooning into the left atrium in systole and a marked doming toward the left ventricle in early diastole. Various parameters related to the production of M1 and OS in group I were significantly increased as compared with those of the other two groups. 3. In group II, the body of the AML was not pliable in spite of mild organic changes in the valve. The degree of early diastolic doming was mild. Compared to group III, the intensity of M1 in group II was significantly larger, but no significant difference was observed in the parameters related to the production of M1 between the two groups.(ABSTRACT TRUNCATED AT 400 WORDS)