The value of radioimmunoassay for creatine kinase BB isoenzyme (CK-BB) determination in early diagnosis of acute myocardial infarction was estimated. The clinical material consisted of 35 randomly selected patients admitted to a coronary care unit during the 4 h after chest pain suspected for myocardial infarction. In all patients standard 12 lead electrocardiograms were obtained on admission and at 24, 48 and 72 hours after admission. Blood samples for CK-BB analysis were collected on admission and at 4 hourly intervals for 48 h after admission. Aspartate aminotransferase (GOT) activity was determined in all patients on admission and in samples obtained at 24 and 48 hours. The patients were classified to 3 groups according to electrocardiographic and clinical findings. The first group consisted of 10 patients whose electrocardiograms fulfilled the criteria of transmural infarction. The electrocardiograms of 10 patients of the second group fulfilled the criteria of subendocardial infarction. The remaining 15 patients made up a third group of coronary insufficiency. The activity of CK-BB at various time intervals after chest pain in all groups was compared in order to estimate the value of this method for differentiation of the 3 causes of coronary pain. The frequency of positive results (the values exceeding upper limits of normal range for healthy people) at various time intervals after pain obtained with both enzymatic methods was compared in order to estimate the sensitivity of analysed method.(ABSTRACT TRUNCATED AT 250 WORDS)