New 2-site labeled monoclonal antibody techniques were used to measure serially plasma levels of brain-type creatine kinase (CK-BB), heart-type creatine kinase (CK-MB) and muscle-type creatine kinase (CK-MM) during a 20-hour postoperative period in 24 infants after deep hypothermia and total circulatory arrest used in pediatric cardiac surgery. A control group of 7 children undergoing cardiovascular procedures without extracorporeal circulation or circulatory arrest also were studied. There were marked increases in CK-MB and CK-BB levels in the circulatory arrest group but not in the closed group. CK-BB increased from 3.2 ± 0.5 to 27 ± 10 ng/ml and CK-MB from 5.9 ± 2.1 to 137 ± 12 ng/ml. The CK-MM concentrations increased from 299 ± 91 and 194 ± 49 ng/ml to 1,220 ± 274 and 1,322 ± 142 ng/ml in the closed and circulatory arrest groups, respectively. Peak levels of CK-MB and CK-BB occurred an average of 133 and 127 minutes, respectively, after reperfusion. The half-time of CK-BB differed significantly from that of CK-MB (149 ± 15 vs 359 ± 20 minutes). The arrest time had a more marked effect on CK-BB concentration than on CK-MB and CK-MM concentrations. Arteriointemal jugular venous concentration differences were consistently negative for CK-BB in the circulatory arrest group, but not for CK-MM and CK-MB. The results indicate that deep hypothermia with total circulatory arrest results in a release of CK-BB into peripheral blood and strongly suggest that the origin of this release is predominantly cerebral and the release of CK-BB occurs in proportion to the severity of the ischemic insult to the brain.