A reproducible noninvasive technique for measuring right ventricular ejection fraction (RVEF) was developed using first pass quantitative radionuclide angiocardiography. Tests were carried out in the right anterior oblique position with a computerized multicrystal scintillation camera with high count rate capabilities. RVEF was calculated on beat to beat basis from the high frequency components of the background-corrected right ventricular time-activity curve. The following results were obtained; 1) In 10 normal adults, RVEF averaged 50.9+/-8.2. In 20 patients with chronic obstructive lung diseases (COPD), RVEF was 37.9+/-6.1% and significantly lower than that of normal persons(P<0.005). 2) There was meaningful correlation between RVEF and forced expiratory volume (FEVI) in patients with COPD (r=0.51). And there was significant difference of RVEF between 13 patients with FEVI less than IL/min (6 patients with right ventricular failure, 7 patients with patients without that) and 7 patients with FEVI IL/min or more (35.7+/-6.0%, 42.1+/-3.2% respectively. P<0.005). 3) All 6 patients with clinical manifestation of right heart failure had abnormal RVEF and had FEVI less than IL/min, which was significantly lower than that of 14 patients without clinical manifestation of right heart failure (33.6+/-4.8%, 39.8+/-5.6%, respectively. P<0.005). 4) In 14 patients without clinical manifestation of right heart failure, 11 patients among whom 7 patients had FEVI less than IL/min, had abnormal RVEF.