[en] The usefulness of a new myocardial perfusion agent, ^99mTc-MIBI, was investigated in 10 patients with clinically suspected ischemic heart disease by comparison with ²⁰¹Tl-SPECT. The MIBI images were clearer than those of Tl in 8 cases and both images were almost the same quality in 2 cases. Liver uptake overlapped on the inferior and posterior walls in only one case at the early (30 min) rest image but it was disappeared at the late (4 h) image. Newly appeared perfusion defect in 4 examinations at the late (4 h) image in spite of no defect at the early (30 min) image indicated that washing out of MIBI also could not be ignored in some cases. All MIBI exercise images were coincident with Tl exercise early images. All MIBI rest images expect for 2 examinations were coincident with Tl delayed images. Although more investigations are necessary for washing out from the myocardium and the difference with Tl findings, we concluded that ^99mTc-MIBI was a promising radiopharmaceutical for myocardial perfusion imaging. (author)