The course of atrophy of the gastrocnemius muscle of the rat was investigated by detn. of excitability, wt., water content, O2-consumption, and total and micellar birefringence. On rats with both legs de-nervated, but with one gastrocnemius stimulated daily with suitable electrical currents, such a treatment was able to retard distinctly the loss in excitability and dry wt., while the already raised metabolism was further increased. However, the loss in birefringence was slight and the loss of power of the treated muscle was less than would be the case if the contractile mechanism were influenced by the treatment to the same extent as the wt. loss. The best results are obtained with electrical stimulation starting immediately after denervation, and with a strength and duration of current adapted to the changing excitability of the atrophying muscle. The failure of the electrical treatment to repair the damaged ultrastructure of the denervated muscle is the main reason why, despite the arrest of atrophy and increased excitability, the treated denervated muscle improves only slightly in power.