Experimental resection of the olfactory nerve in the homing pigeon induced a total degeneration of the nerve and olfactory epithelium. The orthograde degenerative process started before the retrograde one. Ten days after resection, new neurons began to differentiate from the basal cells. The axon formed earlier than the distal dendritic process, and the speed of growth increased slowly. The regenerated axons only reached the bulb in the 5th mo. Two months after resection the olfactory epithelium was similar to that of the intact control side. The ultrastructural features [seen by EM] of the mucosa and olfactory axons are similar to those of normal ones.