Quantitative analysis of dendritic branching patterns was performed in rapid Golgi sections of the lateral geniculate nucleus of Old World monkeys at several ages, using a computer-microscope and a tree-analysing program. In parvocellular and magnocellular multipolar neurons the dendrites were analysed in centrifugal order and according to whether they were intermediate or terminal segments. Between late gestation and birth there is an increase in the mean length of dendrites, and in the total length of dendrites per neuron, more pronounced in magnocellular layers; there follows a progressive decrease in their length until adulthood. However, only terminal dendritic segments are involved in these changes in length. Intermediate segments are shorter and show a more or less constant length throughout life. The final length of a segment seems more determined by it being terminal or intermediate than by its order of branching and there is greater plasticity in the terminal part of the dendritic tree. Magnocellular neurons are characterized by a greater number of both intermediate and terminal segments than parvocellular neurons but not by a greater length of individual segments. This accounts for the greater dendritic length in magnocellular neurons and may offer them a larger surface for synaptic connectivity.