Gastrocnemius muscles from eight adults with moderate to severe denervation of various causes (excluding vascular diseases), along with biopsy specimens from seven controls, were studies in semithin epoxy resin sections and by electron microscopy. Morphometry showed diminution in the number of capillaries per muscle fiber roughly proportional to the degree of muscle fiber atrophy. The number of capillaries per transverse muscle fiber area tended to increase. By phase microscopy, destroyed capillaries were found in all denervated muscle specimens. Denervated muscle becomes relatively overvascularized, and probably as a result, some capillaries become necrotic. This tends to restore the normal equilibrium between muscle mass and blood supply. The capillary changes of denervation can be distinguished from those in dermatomyositis.