Intermittent liberation of the serum marker myoglobin is found in acute myocardial infarction, and the ST segment of the electrocardiogram also shows a phasic rise and fall. We therefore measured the serum marker CK-MB at close intervals of time and recorded an oscillation in the serum level. The peaks are not as high as in the serum myoglobin time curve, and it is not easy to decide if they represent the intermittent liberation of the serum marker. It was possible to distinguish between a "high release" and a "low release" group of patients: the former having a maximum CK-MB value of greater than 100 U/l and the latter of less than 100 U/l. Most patients showed 2-3 "initial peaks" within the first 8 h. The highest of these immediately preceded the climb to the definitive maximum value. We conclude that the small size of the peaks in the CK-MB time curve is due to a different mechanism of enzyme release.