In the first of two groups of rabbits aged less than 7 weeks, the tibialis anterior muscle was permanently denervated by suturing the divided common peroneal (external popliteal) nerve into biceps femoris, while in the second it was temporarily denervated by crushing the nerve. Longitudinal growth of the muscle bellies was diminished so that, by the time the rabbits were almost fully grown, their lengths in the two groups were respectively about 85 and 95% of the normal. The diminution of growth following complete or partial nerve section (with the possibility of reinnervation) lay between these extremes, its extent apparently depending on the duration of denervation and on the extent of reinnervation. The shape of the isometric tetanic tension-length curves of those muscles which became well reinnervated did not differ appreciably from the normal. Small indian ink marks were placed at intervals along the muscle in some of the young rabbits and measurement of the distance between them at the beginning and end of the experiment showed that denervation did not significantly affect the site at which longitudinal growth occurred.