Summary1. Serum transaminase and lactic dehydrogenase levels are excellent tests for detecting tissue necrosis. They can contribute to the diagnosis of myocardial infarction, especially cases where the diagnosis cannot be firmely established on clinical and/or electrocardiographic grounds.2. Only repeated dosages, with the construction of a dosage-time curve, are of diagnostic value (38). A sharp increase in serum enzyme levels followed by a progressive return to normal indicates coronary thrombosis while permanently high values suggest a lesion in some other organ (fig. io). A secondary increase in serum enzyme levels (especially DL) in the course of myocardial infarction is usually due to necrosis within some other tissue (23,24,25,27,29).