Sarcoidosis of the myocardium, an illness occurring predominantly in young adults, frequently becomes clinically apparent when the disease is far advanced. Since the thallium myocardial perfusion scan (TMPS) is known to be capable of detecting granulomas, it seemed to be promising as a noninvasive means of screening for this complication of sarcoidosis. We, therefore, examined 44 consecutive patients with sarcoidosis, none of whom had clinical evidence of heart disease, utilizing TMPS, echocardiography, electrocardiography, systolic time interval ratios (PEP-LVET) and 24-hour Holter monitoring. TMPS disclosed left ventricular defects in 14 patients (32 per cent) and abnormalities of the right ventricle in an additional four patients. Left ventricular abnormalities on the TMPS were associated with echocardiographic evidence of left ventricular dysfunction (widened mitral E point septal separation) but not with abnormalities on Holter monitoring or electrocardiograms. Systolic time interval ratios were insensitive but highly specific for the presence of abnormalities on the TMPS. We conclude that the TMPS frequently discloses abnormalities in sarcoidosis, which may be a reflection of its sensitivity in this setting.