Serum samples from 14 men and 8 women were obtained pre-marathon (48 h) and at 24, 48, 72, and 96 h post-race to quantitate total serum creatine kinase activity (TCK), percentage of creatine kinase MB (CK-MB), and clearance rates (half-lives) of TCK and CK-MB. TCK was measured enzymatically, and the CK-MB isoenzyme was separated by agarose electrophoresis and quantitated by densitometry. The men's and women's post-race mean TCK levels were significantly elevated (P less than 0.05) above pre-race values at 24 h (3322 U . l-1, 946 U . l-1 and 48 h (1787 U . l-1, 508 U . l-1). In addition, CK-MB was significantly elevated both 24 h (5.1%, 3.3%) and 48 h (2.5%, 1.8%) post-race (P less than 0.05). The men's 24-h TCK was 22.3 times the pre-race value, while the women had an 8.6-fold increase in TCK. The mean 24-h post-race CK-MB activities were 166 U . l-1 for the men and 31 U . l-1 for the women. The mean increase in CK-MB activity was 41.5-fold for the men and 7.8-fold for the women. Furthermore, the men had a mean half-life (t1/2) of 30.4 h for TCK and 12.0 h for CK-MB; the women's t1/2's were 29.4 and 16.8 h, respectively. At all time points, the men evidenced significantly (P less than 0.05) higher TCK and CK-MB enzyme activities than did the women.(ABSTRACT TRUNCATED AT 250 WORDS)