Mid-ventricular obstruction was evaluated in a case of hypertrophic cardiomyopathy using a real-time two-dimensional Doppler flow imaging system. A 60-year-old woman was referred to our hospital because of oppressive precordial sensation., I-mode echocardiography showed asymmetric septal hypertrophy: thickness of the end-diastolic left ventricular posterior wall was 9 mm, and that of the interventricular septum was 19 mm. However, there was no systolic anterior motion of the mitral apparatus. Doppler color flow imaging showed a mid-left ventricular narrowing in late-systole and a mosaic pattern was depicted from the mid-ventricle to the outflow tract. Continuous wave Doppler echocardiography disclosed a peak velocity of 2.0 m/sec (pressure gradient (PG) = 16 mmHg). In the right ventricular outflow tract, a mosaic pattern was also seen and a peak velocity of 1.5 m/sec was detected (PG = 9 mmHg). These results were nearly identical with the data measured by cardiac catheterization. Thus, it was concluded that intraventricular obstruction of hypertrophic cardiomyopathy is diagnosed by observing the flow image and flow velocities in the ventricle using a real-time two-dimensional Doppler flow imaging system.