Direct monitoring of myoglobin efflux during the ischemic and reperfusion periods has been limited because of inherent sample collection problems in the ischemic region. Recently, cardiac dialysis technique has offered a powerful method for monitoring myocardial interstitial levels of low molecular compounds in the cardiac ischemic region. In the present study, we extended the molecular target to high molecular compounds by microdialysis probes with a high molecular mass cut-off and monitored myocardial interstitial myoglobin levels. We implanted a dialysis probe in the left ventricular free wall in anesthetized rabbits. The main coronary artery was occluded for 60 or 120 min. We examined the effects of myocardial ischemia and reperfusion on myocardial interstitial myoglobin levels. The interstitial myoglobin increased within 15 min-ischemia and continued to increase during 120 min-ischemia, whereas the blood myoglobin increased at 45 min-ischemia. The increases in lactate and myoglobin appeared in the interstitial space during the same period. At 60 min-ischemia, reperfusion markedly accelerated interstitial myoglobin release. The interstitial myoglobin level at 0-15 min of reperfusion was 5-fold higher than that of the same period of coronary occlusion. The dialysis technique permits earlier detection of myoglobin release and separately monitors its release during ischemic and reperfusion periods. Myocardial interstitial myoglobin levels can serve as an index of myocardial injury evoked by ischemia or reperfusion.