Eighty-seven patients (64 females and 23 males) with mitral stenosis were studied by M-mode echocardiography to assess the sensitivity and the specificity of the echocardiographic technique in the identification of valve calcification. The mitral valves were examined at operation, and the amounts of calcium were graded as heavy, light, or absent. We compared this with the amount of calcification assessed by radiographic, previously accepted echocardiographic, and newly derived echocardiographic criteria. In identifying the presence or absence of valve calcification, radiography was the least sensitive (53.7 per cent), but the most specific (90.9 per cent) technique, and has the highest predictive accuracy (90.6 per cent). Previously accepted echocardiographic criteria had the highest sensitivity (92.6 per cent), but the lowest specificity (12.1 per cent), and the lowest predictive accuracy (63.3 per cent). The newly derived echocardiographic parameter MT/ST (ratio between the maximal thickness of the left ventricular margin of the interventricular septum) was both sensitive (75.9 per cent) and specific (81.8 per cent) and also had a predictive accuracy (87.2 per cent) similar to that of radiographic techniques. The MT/ST ratio is demonstrated to be the most useful non-invasive method for assessing valve calcification in mitral stenosis.