Abstract Mitochondria from denervated muscles were examined for a number of biochemical variables. Starting from the third day after nerve section, they exhibited a decreased ability to carry out the oxidation of α-ketoglutarate, l-glutamate, and pyruvate, together with a diminution of the cytochrome oxidase activity. The decrease of the cytochrome oxidase activity was much more evident if measured in the whole homogenate. The phosphorylative efficiency of mitochondria from denervated muscles, as judged by the P:O ratio and respiratory control index, was unaffected. The obtained results point to a process of impoverishment of the enzymes of both the mitochondrial membrane and matrix. This process is accompanied by the disappearance of the mitochondria. The relevance of these findings to the problem of the pathogenesis of muscle denervation atrophy is discussed.