A diagonal branch of the left anterior descending artery was occluded for 80 min. One microdialysis probe was inserted in the ischaemic area and two in the non-ischaemic areas. In six animals radiolabelled microspheres were injected before and during ischaemia and after reperfusion to monitor flow. Arterial and pulmonary artery pressures, pulmonary capillary wedge pressure and cardiac output were followed-up. Radiolabelled microsphere distribution confirmed the reduction of myocardial blood flow during coronary artery occlusion, with flow returning to normal values upon reperfusion. Rate pressure product as an index of heart work was stable throughout the 80 min ischaemic period, but increased at reperfusion. Dialysates from non-ischaemic tissue showed stable baseline values. In ischaemic tissue, lactate increased by 300% and pyruvate levels decreased by 50% within 15 min. Adenosine increased rapidly five-fold, but started to decline after 15 min of ischaemia. Inosine showed a slower but a marked 20-fold increase, decreasing at the end of the ischaemic period. Hypoxanthine increased five-fold during the first 30 min. Finally, guanosine showed a slow increase to about four times above basic values. Microdialysis was an excellent tool for the continuous monitoring of myocardial metabolites during ischaemia. Adenosine appeared to be a more sensitive marker of early ischaemia than lactate, although interestingly, adenosine levels had decreased already after 15 min, most probably due to intracellular accumulation of protons and Pi.