Serum levels of creatine phosphokinase isoenzyme pattern (CPK MM, MB, BB) were measured in cord blood and capillary blood samples of 20 healthy term infants. Total CPK activity was high but similar in all samples, the main source being derived from the CPK-MM fraction. The CPK-MB fraction was absent in cord blood. Moreover, CPK-BB activity was significantly higher in capillary blood than in cord blood. These results suggest specific organ involvement in the production of CPK fractions.