A close mutual relationship between the processes of oxidation and oxidative phosphoryiation and the maintenance of the structural integrity of mitochondria (1) has been proposed. By use of the high energy phosphate bonds generated during the metabolism, the mitochondria contribute for some time to their self preservation. It is, however, very probable that other cellular structures, which lack the means of elaborating ~-~P,~ also utilize the energy provided by the mitochondrial metabolism for their structure and function. There are, however, no available studies which provide information that the mitochondria supply N p directly to other structures in order to maintain them. The present studies deal with the occurrence of such a relationship in skeletal muscle between the cytochondria (2) and the myofibrils.Since the pioneer physiological studies of Ranvier (3) and BonhSffer (4), and the later metabolic work of Battelli and Stern (5), it has been realized that the difference in structure of muscles is associated with a difference in function and oxidative capacity. Stare and Baumann (6) later catalogued several of the outstanding variations among muscles and established the high