Thirteen kits from different suppliers for measurement of creatine kinase activity in human serum according to the IFCC recommendations were analyzed and compared. Concentrations of AMP, ADP, creatine phosphate, glucose, magnesium ion, NADP<sup>+</sup>, glucose-6-phosphate dehydrogenase, hexokinase and pH were measured in the reagents by various analytical techniques and compared with those recommended by the IFCC. We also compared by regression analysis the results of creatine kinase catalytic concentration obtained in human sera using commercial kits and in-house prepared reagents according to the IFCC recommendation. Creatine kinase was also measured in a reference material using the different reagents. The overall results of the activity measurements and the composition of the majority of the kits agree well with one another and with the IFCC recommendation. Minor deviations were found in the evaluation of a few kits. One kit yielded creatine kinase activity values that were 17% lower. Results obtained in the reference material measurements showed differences with some kits which were not found using human sera. © 1995 Walter de Gruyter & Co.