To evaluate the usefulness of radionuclide cardiac angiography in the assessment of right ventricular function, we measured right ventricular ejection fraction (RVEF) using single pass method. In 12 normal persons, RVEF averaged $52.7{pm}5.9%(mean{pm}S.D.)$. In 25 patients with chronic obstructive lung disease, RVEF was $37.2{pm}10.6%$ and significantly lower than that of normal persons (p<0.01). All 10 patients with right ventricular failure had abnormal RVEF, which was significantly lower than that of 14 patients without right ventricular failure ($27.6{pm}5.7%,;43.9{pm}8.5%$, respectively. p<0.01). It concluded thal RVEF measured by single pass radionuclide cardiac angiography was a useful, noninvasive method to assess right ventricular function.