Duplex Doppler echocardiography with high pulse repetition frequency was used to study: group A - 7 patients with mitral stenosis (MS) during cardiac catheterization, and group B - 26 patients with MS in whom the Doppler examination was performed 24 h-3 months prior to catheterization. Using the peak flow velocity within the stenotic flow jet, the pressure drop and mitral valve area (MVA) were calculated and compared with data obtained invasively. The inter-observer variability of the two parameters was 12% and 5%, respectively. The correlation between Doppler pressure drop and invasive measurement was excellent in group A (r = 0.83), while less close in group B (r = 0.71). However, using only MVA estimates (group B), it was possible to recognize most of MS with catheterization MVA less than or equal to 1.0 cm2/m2 (sensitivity and predictive value both of 90%). Therefore, even nonsimultaneous quantitation of MS seems valuable in pre-operative patient evaluation, adding a new information to hitherto existing echocardiographic criteria.