This study was aimed at estimating mean transmitral gradients by simultaneous Doppler echocardiography and cardiac catheterisation and determining mitral valve area by pressure half time, Gorlin's formula and two-dimensional echocardiography so as to assess the relative accuracy of these methods before and after balloon mitral valvuloplasty in patients with rheumatic mitral stenosis. Left atrium-left ventricular, pulmonary artery wedge-left ventricular and echo gradients were simultaneously recorded in 18 patients undergoing balloon mitral valvuloplasty. Mitral valve area was estimated by pressure half time, Gorlin's equation and two-dimensional echocardiography. The correlation between left atrium-left ventricular and echo mean gradient before balloon mitral valvuloplasty was 0.96 (p < 0.03). Between pulmonary artery wedge-left ventricular and echo mean gradient, it was 0.95 (p < 0.04). The correlations between left atrium-left ventricular and pulmonary artery wedge-left ventricular mean gradient were also good. After balloon mitral valvuloplasty, similar good correlations were seen. On subgrouping the patients into those with high and low pulmonary artery pressure, good correlation persisted both before and after balloon mitral valvuloplasty. Mitral valve area by all the methods were similar before balloon mitral valvuloplasty. After balloon mitral valvuloplasty, mitral valve area by pressure half time was the least and by two-dimensional echocardiography, the maximum. All the three methods are equally accurate in estimating transmitral gradients and mitral valve area in mitral stenosis before balloon mitral valvuloplasty. Two-dimensional echocardiography is the best to estimate mitral valve area after balloon mitral valvuloplasty. Echocardiography can replace haemodynamic measurement of gradients and mitral valve area before and after balloon mitral valvuloplasty. But pressure half time is not recommended for measuring mitral valve area immediately after balloon mitral valvuloplasty where two-dimensional echocardiography mitral valve area is to be employed.