The retrograde nerve cell reaction was studied after crush lesion of the facial nerve in rats of different ages. Neuronal survival increased from 10% in newborn rats to 100% in adults. In 8- or 10-day-old animals axotomy caused central chromatolysis, nuclear eccentricity, folding of the nuclear membrane, and development of nuclear caps. Similar lesions in adult rats caused only minimal changes. The findings differ from those previously reported in hamsters [La Velle and La Velle, 1958a, b, 1959], where chromatolysis was most severe in adult animals. However, the neuronal survival followed the same age-related pattern in rats and hamsters. Thus, there are marked species differences in the chromatolytic response after axotomy, but these differences do not affect neuronal survival. It is concluded that chromatolysis is not a decisive factor for neuronal recovery after axon injury in young animals.