For quantitative evaluation of acute myocardial infarction, In-111 antimyosin Fab myocardial imaging (InAM) was performed in 17 patients with myocardial infarction who underwent Tl-201 (TL) and Tc-99m pyrophosphate (PYP) myocardial imaging in acute phase. For calculating the infarct size, voxel counter method was used for analysis in PYP and InAM, and extent and severity score were used on bull's-eye polar map in TL. The most appropriate cut-off level ranged from 65 to 80% by the fundamental experiment using cardiac phantom. The cut-off level of 0.70 (InAM) and 0.65 (PYP) were used for clinical application of voxel counter analysis. The infarct size calculated by InAM and PYP was compared with wall motion abnormality index by echocardiography (WMAI), TL extent score, TL severity score, peak CK and sigma CK. Infarct size by InAM showed the following correlations with other indices. PYP: r = 0.26 (ns), TL extent score: r = 0.72 (p less than 0.01), TL severity score: r = 0.65 (p less than 0.05), WMAI: r = 0.69 (p less than 0.05). The infarct size by PYP did not show any correlations with these indices. Therefore, the infarct size by InAM showed better correlations with TL and WMAI than that of PYP. So InAM was considered superior to PYP for quantitative evaluation of acute myocardial infarction.