Metabolic imaging using 123I-labeled 15-(p-iodophenyl)-3-R,S-methylpentadecanoic acid (BMIPP) and Fourier phase analysis of gated blood-pool data were performed in a 60-yr-old woman with idiopathic hypertrophic cardiomyopathy. Dyskinetic wall motion was identified as a markedly delayed phase angle in the left ventricular apex, which was well perfused but highly hypertrophied like other ventricular segments. Fatty acid imaging, however, clearly demonstrated highly reduced activities in the apex, although there were no abnormalities in regional systolic function or in 201TI uptake in other hypertrophied regions. Contrast left ventriculography revealed a midventricular collapse of the left ventricle at end-systole due to markedly hypertrophied ventricular walls and dyskinesis at the apex. Thus, dyskinetic wall motion in the apex closely correlated not only with cardiac hypertrophy but also with impaired fatty acid uptake. These findings were unrelated to the myocardial perfusion state per se. Fatty acid imaging using BMIPP may contribute to the detection of myocyte degeneration not visible using conventional imaging modalities. It may also provide etiological information on regional dysfunction in hypertrophic cardiomyopathy.