This study was conducted to evaluate the postnatal changes of serum creatine kinase (CK) and its isoenzymes in normal and asphyxiated newborns. In normal newborns total CK, CK-MM and CK-MB reached a plateau between 2 and 24 hr after birth whereas the serum CK-BB remained stable after birth. CK-MM, CK-MB and CK-BB respectivily composed 90~94%, 5~7% and 1~5% of total CK during study period. In asphyxiated newborns total CK, CK-MM and CK-MB reached maximal value at 12 hr after birth whereas CK-BB decreased after birth. There were no significant differences between normal and asphyxiated newborns in total CK, CK-MM and CK-MB during study period (up to 24 hrs after birth). But CK-BB of asphyxiated newborn was elevated significantly (p<0.05) within 6 hrs after birth compared to normal newborns. There were no significant differences of CK and its isoenzymes between patients evaluated by 5 min Apgar scores(0~3, 4~6 and 7~10) or degree of HIE (HIE stage 0~I, II and III). According to these results, the serum CK-BB is elevated in asphyxiated newborns during 1st 6hrs after birth but has no predictive values of the extent of cerebral damage.