Radiolabeled fatty acids such as iodine-123-betamethyl-p-iodophenyl-pentadecanoic acid (BMIPP) have unique metabolic properties suggesting potential use as myocardial perfusion tracers. The uptakes of BMIPP and thallium 201 were compared using single photon emission computed tomography (SPECT) in 24 patients displaying unstable angina with multivessel disease at a mean of 3.4 days after admission. Coronary angiography was performed within a week. Uptake was considered normal if the activity was greater than 80% of the normal area, mildly reduced if 50% to 79%, and severely reduced if less than 50%. The regional activities in four quardrants in short-axis slices were measured from basal, mid and apical sets. We attempted to identify the causative lesion on dual SPECT imaging. We planned the following management of each patient based on the results of the dual SPECT study. BMIPP activity imaging found 4 segments (1.4%) with severe decrease, 70 (24.3%) with mild decrease, and 214 (74.3%) with normal uptake. In contrast, T1 activity imaging showed normal uptake in 68 of 74 abnormal BMIPP activity segments. Furthermore, all segments with abnormal BMIPP uptake were matched with locations of coronary artery stenosis by coronary angiography. Accordingly, coronary revascularization (percutaneous transluminal coronary angioplasty, coronary artery bypass grafting) was performed based on BMIPP SPECT. Reductions in BMIPP activity were common in patients with unstable angina with multivessel disease. BMIPP SPECT is an excellent tool for detecting the causative lesion in unstable angina. The subsequent intervention could be performed with less risk based on the strategy of dilating the only causative lesion which was detected by the BMIPP SPECT in patients with multivessel disease displaying unstable angina.