Developmental changes in spherical cell sizes were measured in the ventral cochlear nucleus (VCN) in normal guinea pigs aged 2 days and 2, 7 and 12 weeks to establish the time course of postnatal neuronal growth, as a baseline for our experimental work. A continued growth of spherical cell size was observed in the VCN up to 7 weeks postnatally. Animals were unilaterally deafened by cochlear perfusion with kanamycin sulphate at ages 1 and 6 weeks. After 6 weeks survival the spherical cells were measured in the VCNs of both sides. Unilateral deafferentation at both ages caused an ipsilateral reduction in spherical cell size, neurons of the younger group being smaller than in the older. On the contralateral side these cells in the older group were larger than age-matched controls while in the younger group there was no difference compared with age-matched controls. These findings suggest that the results of deafferentation are age-dependent, and may indicate an ability of the neural circuitry to adapt to the loss of sensory input on the other side.