Serum creatine kinase (CK) and creatine kinase-MB isoenzyme (CK-MB) activities were studied prospectively in serial blood samples obtained from 23 perinatally asphyxiated negroid newborns and 12 healthy controls during the first 100 h of life. The asphyxiated infants had significantly elevated mean CK and absolute CK-MB but no fractional CK-MB activities. Peak mean CK and CK-MB values (U.l-1) were 789.17 (+/- 220), P less than 0.01 and 16.36 (+/- 3.0) P less than 0.001 respectively at the 6-8 post-partum period. The healthy controls, on the other hand, showed a steady decline in the activities of these enzymes from birth. The vaginally and operatively delivered asphyxiated infants showed significantly higher CK and CK-MB activities than their respective non-asphyxiated controls, but no increase in fractional CK-MB was recorded in any of the groups. The elevation in absolute and fractional CK-MB 42.0 U.l-1 (5.1%) in respect of the infants with TTI (transient tricuspid incompetence) was significant (P less than 0.05) when compared with the controls with features of TTN (transient tachypnoea of the newborn) in the 6-8 h post-partum period. One of the infants with TTI at autopsy had hypoxic myocardial injury. The specificity of CK-MB, as a marker of myocardial injury in asphyxiated negroid neonates, is plausible but remains uncertain. Until the lack of rise of CK and CK-MB in healthy negroid newborns is confirmed in a larger series with further studies on MM, BB and MB isoenzymes, caution is urged in the interpretation of elevated CK and CK-MB activities in asphyxiated negroid newborns.