Echocardiographic studies were performed both before and after commissurotomy on fifteen subjects affected by non-calcified mitral stenosis. The amplitude CE of the anterior leaflet dis placement, the slope of the CD and EF intervals, the amplitude of the A-wave, the ratio FA/DE and the reciprocal position of the anterior and posterior leaflet echoes were measured on the echographic records. These data were compared with the values obtained in ten normal subjects. After commissurotomy, the slope of the CD interval and most evidently that of the EF interval increased (the last one by a factor of 3), and the area of the mitral opening was found to be more than 9% larger. The A-wave reappeared clearly in 30% of the operated patients, and the outline of the posterior leaflet was no longer inscribed in the anterior leaflet diastolic curve in all cases; the amplitude CE was unchanged.