The fate of skeletal muscle-derived creatine kinase (CK) was investigated in six dogs. After i.m. and i.v. injections of 3000 g and 105 000 g supernatants of dog muscle homogenates, plasma CK activity was measured up to 48 h. There was no significant difference in pharmacokinetic parameters dependent on the type of supernatant injected. After i.v. injection, the volume of distribution of CK was equal to the plasma volume, CK clearance was relatively low (about 0.5 mL/kg/min) and its terminal half-life of elimination was about 2.5 h. After i.m. injection, the CK terminal half-life was about 6.5 h, demonstrating a flip-flop mechanism, i.e. a limiting absorption process from the site of injection. Bioavailability after i.m. injection was about 65%, and the rate of absorption from muscle injection site was relatively slow: peak activity occurred at the second hour post administration, and most CK activity had been absorbed by 24 h. These pharmacokinetic parameters can be used as a basis for a minimally invasive means of quantitating muscle damage either after intramuscular drug administration or in canine sports medicine.