The aim of this study was to compare the results of unidimensional and cross-sectional echocardiography and cardiac catheterisation in the assessment of mitral and aortic stenosis. 21 patients with mitral stenosis, 21 patients with aortic stenosis and 21 patients without valvular disease were studied by unidimensional and cross-sectional echocardiography and cardiac catheterisation. Although unidimensional echocardiography in the external cardiac investigation of choice for the qualitative diagnosis of mitral stenosis, a better assessment of the severity of the stenosis is obtained with cross-sectional echocardiography. The valve surface measured by cross-sectional echocardiography correlates well with the value obtained by catheterisation with the application of the Gorlin formula (r = 0.85). Cross-sectional echocardiography is therefore an important advance in the external assessment of mitral stenosis. The aortic valve can only be measured in one third of cases of aortic stenosis with unidimensional echocardiography, whilst this measurement can be performed in 90 p. 100 of cases with cross-sectional echocardiography. The values obtained in 9 patients with severe aortic stenosis were 3.7 +/- 0.7 mm/m2, in 7 patients with moderate aortic stenosis: 5.4 +/- 0.8 mm/m2 and in 5 patients with mild aortic stenosis: 6.8 +/- 1,2 mm/m2. There is a clear demarcation between the different groups if the average values are compared. Therefore cross-sectional echocardiography gives reliable semi-quantitative assessment of the severity of aortic stenosis.