The distribution of a new myocardial fatty acid metabolic agent123I-BMIPP was compared in 6 of each patients with hypertrophic myocardium (4 cases of hypertensive heart disease and 2 of hypertrophic cardiomyopathy) and dilated myocardium (4 of dilated type of valvular heart disease and 2 of dilated cardiomyopathy) with that of201Tl. Mismatched regional myocardial uptake between123I-BMIPP and201Tl SPECT was observed in all of the hypertrophic myocardium, however no but one in the dilated myocardium. Relative increase or decrease in regional BMIPP from the images of 20 min and to those of 4 h was observed in 3 cases of the hypertrophic myocardium. FDGPET was performed in 2 cases of the hyper-trophic myocardium. The distribution of FDG was different from neither those of BMIPP nor Ti in a hypertrophic cardiomyopathy case with the reversed distribution of BMIPP and Tl. Although more investigations are necessary, we concluded that123I-BMIPP is a promising radiopharmaceutical for evaluating myocardial fatty acid metabolism in hypertrophic myocardium.