Satellite cells exhibit a number of distinct morphological changes after denervation which appear to be a direct response to nerve section or altered functional state of the muscle fibers. These changes appear generally related to increased movement and overall activation of the cells. After longer periods of denervation many satellite cells appear to separate from their fibers and become free cells in the interstitial space. It is proposed that this mechanism provides a cellular source for the small-diameter, immature fibers dispersed throughout the muscle after two to three weeks. Although neo-formation of myofibers appears to be a feature of denervated growing muscle, an increase in total fiber population was not observed. It is suggested that in the absence of a viable nerve supply the new fibers degenerate.