The activity of glycogen phosphorylase (GP) and creatine phosphokinase isoenzyme MB (CPK MB) was measured in patients with myocardial infarction over 72 hours after the anginal attack. In most clinical observations, CPK MB and GP patterns were similar, however, the GP activity reached its peak 4-6 hours earlier, and sooner returned to normal, as compared to that of CPK MB. The measurement of GP and CPK MB activity at early dates of myocardial infarction provides more evidence of new lesion foci or expanding necrotic area. In one-third of the infarction patients, the said enzymes showed different patterns of activity. It is suggested that the assessment of GP and CPK MB activity in cases of myocardial infarction may contribute to better insight into both necrotic and ischemic myocardial processes associated with myocardial infarction, with similar trends in enzyme patterns indicating necrotic myocardial changes, and high GP activity coupled with unchanged CPK MB signalling myocardial ischemia.