The sensitivity and specificity of pulsed Doppler echocardiography (PDE) in diagnosis and estimation of the severity of mitral regurgitation in the presence of rheumatic mitral stenosis was studied in 34 patients (18 women and 16 men) ranging in age from 33 to 70 years (mean 55). Definitive diagnosis of mitral regurgitation was confirmed in all patients by angiography and in 20 patients also by indicator dilution technique. Mitral regurgitation was detected by PDE in all patients with angiographically proven severe mitral regurgitation and in 7 of 8 patients with moderate mitral regurgitation. In patients with trace to mild mitral regurgitation, PDE was positive in only 7 of 13 patients. When subdivided for mild, moderate and severe mitral regurgitation, PDE sensitivity for diagnosis was 54, 88, and 100%, respectively; overall accuracy was 79% and specificity was 100%. Average systolic dispersion on time-interval histogram was 59% for mild, 89% for moderate, and 100% for severe mitral regurgitation. Groups of patients with mild mitral regurgitation could be differentiated from those with moderate (p less than 0.05) and severe (p less than 0.01) mitral regurgitation. A significant overlap of individual values, however, occurred. In 7 of 11 patients with moderate to severe mitral regurgitation, systolic turbulence also was detected in the left atrium. PDE was sensitive and specific in diagnosing moderate to severe mitral regurgitation in the presence of mitral stenosis. Assessment of precise severity of mitral regurgitation is still a problem in individual patients.