Persistent uptake of indium-111-antimyosin monoclonal antibody in patients with myocardial infarction. Indium-111(111In)-antimyosin scintigraphy was investigated in 27 patients with myocardial infarction. 111In-antimyosin Fab was administered intravenously, and planar and single photon emission computed tomographic images were obtained 48 hours later. Uptake of 111In-antimyosin was present in 9 of 10 patients (90%) studied within 6 days of infarction. During the second week positive scans were seen in 16 of 16 patients (100%) including 13 (81%) who had normal creatine kinase levels. The mechanism of persistent positive antimyosin images in the subacute stage of myocardial infarction remains to be clarified. 111In-antimyosin scintigraphy may be useful as a noninvasive method for the detection of myocardial injury late and early after a suspected acute myocardial infarction. 