Gated magnetic resonance tomography (MRT) was conducted in 40 patients (13 normal volunteers, 9 hypertensives and 18 patients with hypertrophic cardiomyopathy) using a 0.35 Tesla superconducting magnet. Multisectional spin echo imaging (35/400 msec) was obtained in coronal, transversal and sagittal planes. Myocardial wall thickness was measured in different segments and the three groups were compared to each other. 15/18 patients with hypertrophic cardiomyopathy (HCM) had asymmetrical regional thickening involving the septum and the anterior wall, in 8/15 the lateral wall was also hypertrophic. The distribution pattern in 3/15 patients with HCM was symmetric. Involvement of the right ventricle was found in 14/18 patients with HCM. There were significant differences (p less than 0.001) in wall thickness for the septal segment in all three groups and for the ratio septal to posterior wall between the HCM and the hypertensives and the normal volunteers. We conclude that MRT can differentiate HCM from hypertensives and normals, and is superior to echocardiographic imaging in the evaluation of the distribution of left ventricular hypertrophy in hypertrophic cardiomyopathy.