The postnatal differentiation of neurons in the dorsal lateral geniculate nucleus of the albino rat was studied using the Golgi-Cox technique. At least four animals were used at postnatal ages 12 hours, 2, 4, 6, 8, 10, 11, 12, 13, 14, 15, 16, 18, 20, 24, 28, 35 days and adult. Presumptive thalamo-cortical projection cells (Class A cells of Grossman et al., '73) and non-projection, intrinsic neurons (Class B cells) are distinguishable at 12 hours after birth. At this stage both types of neuron are immature, with prominent growth cones at their dendritic extremities. Dendritic growth and differentiation appear to be complete by 18 days. Relay cells display two apparent "growth spurts" characterized by noticeable enlargement of the perikaryon and a marked increase in dendritic length and complexity. One occurs between days 4 and 6 and coincides with a period of enhanced synaptogenesis and gliogenesis: the second occurs between days 14 and 15, around the time of eye opening (day 14) and may be related to a further phase of increased synaptogenesis and gliogenesis (Karlsson, '67; Biesold et al., '76). Class B cells appear to "lag" behind class A cells in their initial postnatal differentiation, but also reach their mature condition by day 18.