Postmortem storage of bovine and porcinesemimembranosus muscle under refrigeration (+2 °C) for 14 days did not result in a significant decrease of the total activity of the mitochondrial enzymes citrate synthase andß-Hdroxyacyl-CoA-dehydrogenase, but caused a loss of the activity of lipoamide dehydrogenase. During storage of the muscle tissue there was no detectable release of the three enzymes from the mitochondria into the sarcoplasmic fluid. Therefore, storage of muscle under the conditions used seems not to result in any remarkable damage of the inner membrane of the mitochondrion.