Effects of reperfusion by intra-coronary thrombolysis (ICT) or percutaneous transluminal coronary angioplasty (PTCA) on the myocardial imaging using 111In-labeled antimyosin monoclonal antibody Fab (In-AM) were studied. Reperfusion by ICT or PTCA was done in 16 patients (reperfusion group) and recanalization was seen in 14. Positive images were obtained in 28 of 30 patients (93%) with acute myocardial infarction (onset to imaging: 9.9 +/- 9.8 days). Among the reperfusion group, one patient in whom PTCA was done early after the onset of chest pain and CPK did not elevate showed no significant uptake of radioactivity at cardiac region, while other 15 patients with elevation of CPK demonstrated positive images. Planar images (anterior, left anterior oblique 45 degrees, left lateral) were divided into 15 segments and infarct size (antimyosin-segment) was determined by sum of positive segments on each image. There were no significance between the infarct size in the reperfusion group (7.2 +/- 2.9) and that in the non-reperfusion group (6.9 +/- 3.4). Intensity of the accumulation of radioactivity in each image was classified into 5 grades by comparison with uptake of the liver (antimyosin-score). Reperfusion group demonstrated high intensity compared with non-reperfusion group (2.6 +/- 0.7 vs. 2.0 +/- 0.4; p less than 0.05). Thus, In-AM imaging may be influenced by coronary blood flow, which should be taken into consideration in the interpretation of In-AM imaging.