In order to ascertain whether antimyosin myocardial imaging is superior to the more conventional cardiac radiophosphate scanning for the diagnosis of non Q wave acute myocardial infarction (AMI), we conducted a comparative study with the contemporary use of both tracers. Forty eight patients admitted to the coronary care unit of our centre because of non Q AMI, were included. Between two and seven days after onset, cardiac scintigraphy was performed both using 99mTc labelled diphosphonic-propane-dicarboxylic acid (99mTc-DPD) and 111indium labelled antimyosin (111In-AAM). In addition to planar imaging, tomoscintigraphy (SPECT) with 99mTc-DPD was obtained in 12 patients. 99mTc-DPD imaging was positive for AMI in 44% of the cases, while 111In-AAM in 52% (NS). In most positive cases (more than 85%) myocardial necrosis was localised in the posterolateral wall. In the subgroup of SPECT imaged patients, the percentage of positive findings was the same as the percentage using planar 111In-AAM imaging (58%). We conclude that the apparent efficacy of antimyosin for the diagnosis of non Q AMI is similar to that of 99mTc-DPD imaging. We feel that owing to its higher cost, such procedure should be saved for those cases were standard 99mTc-DPD imaging fails to detect the infarcted myocardium.