Human heart fatty acid-binding protein (FABP) is an abundant low molecular weight protein in cytoplasm of myocardial cell similar to myoglobin (Mb). To evaluate whether FABP can also detect successful reperfusion very early like Mb, we examined serum FABP and Mb levels in 45 patients (pts) undergoing PTCR or PTCA within 6 hours after the onset of acute myocardial infarction. Coronary angiography was performed every 5 minutes (min) during reperfusion therapy to determine the exact time of reperfusion. In 30 pts with reperfusion (reperfused group: TIMI grade 3 [23 pts] and grade 2 [7 pts]), serum samples were taken just before and at 15, 30 and 60 min after initial angiographic confirmation of reperfusion. In 15 pts without reperfusion (nonreperfused group), serum samples were taken just before and at 15, 30 and 60 min after the initiation of therapy. FABP was measured by competitive enzyme immunoassay and Mb by latex agglutination turbidimetry. The FABP ratio (FABP after/FABP before) and Mb ratio (Mb after/Mb before) were calculated. FABP and Mb levels increased rapidly, peaked within 60 min after reperfusion. The FABP and Mb ratios in the reperfused group significantly (p < 0.01) exceeded those in the nonreperfused group at 15, 30 and 60 min. The sensitivity (Sen) and specificity (Spe) of these markers for reperfusion were as follows: Criteria 15 min 30 min 60 min Sen Spe Sen Spe Sen Spe FABP ratio > 1.6 * 93% 100% 97% 100% 100% 100% Mb ratio > 2.4 ** 90% 100% 93% 100% 100% 100% * mean + 2SD at 60 min in the nonreperfused group ** published criteria Conclusion FABP, like Mb could accurately detect successful reperfusion as early as 15 min after reperfusion and could provide a high level of accuracy within 60 min after reperfusion.