This study retrospectively examined a consecutive series of patient CKMB samples for a relationship between age (242 subjects, aged from 20 to 96 years old), serum CKMB activity and corresponding mass results analyzed for CKMB-specific activity (activity per molecule, unit/mg). Patients were categorized into six age groups. The means for specific activity of CKMB, standard error and 95% confidence intervals of each group were calculated. CKMB-specific activity in human serum increases with age regardless of gender or MI severity. As this greater propensity for increased CKMB activity may be due to alteration in part due to protein modification of post-MI release in the blood circulation, these findings add further weight for the current move to the use of troponins and other markers of myocardial injury.