The axonal sprouting that occurs after denervation resulting from a spinal hemisection can be quantified. Rats were subjected to hemisection of the spinal cord at birth, and the myelinated and unmyelinated axons in dorsal roots three segments cranial and three segments caudal to the lesion were counted 1 month after surgery. The number of unmyelinated axons in the dorsal root on the side of the hemisection increased 22 percent for the roots one segment from the lesion and 13 percent for the roots two and three segments from the lesion.