To assess whether regionally depressed myocardial uptake of beta-methyl-p-(123I)-iodophenyl-pentadecanoic acid (123I-BMIPP), is related to regional ventricular diastolic dysfunction in patients (pts) with hypertrophic cardiomyopathy (HCM), we carried out 123I-BMIPP myocardial SPECT and radionuclide ventriculography (RNV) at rest in 9 HCM pts (eight pts with asymmetric septal hypertrophy (ASH), and one patient with apical hypertrophy). The defects of 123I-BMIPP were semiquantitatively estimated by segmental analysis. Regional LV function was determined by sector analysis in RNV: regional peak filling rate (rPFR), regional time to peak filling rate (rTPFR), and early 1/3 filling rate (1/3 fil) were estimated in the LV septal and posterior sectors. Wall thickness was evaluated with M-mode echocardiography. As results, the defects of 123I-BMIPP myocardial SPECT, were found frequently in septal wall, but any defect was not recognized in all septum with significant hypertrophy. Also, the degree of septal hypertrophy was not significantly related to BMIPP defect score. However, the regional diastolic function (rPFR, rTPFR, 1/3 fil) in the septal lesions with 123I-BMIPP defects was decreased more than those without 123I-BMIPP defect in HCM. Furthermore, the relative regional diastolic dysfunction (the differences between rTPFR and 1/3 fil in the septum and in the posterior wall) was significantly related to BMIPP defect score. In conclusion, this results suggest that the decreased uptake of 123I-BMIPP is related to regional diastolic dysfunction more than wall hypertrophy.