The effects of nerve growth factor (NGF) on the three-dimensional structure of newborn rat dorsal root ganglion (DRG) neurons, in vitro, were examined by scanning electron microscopy. Throughout the culture in both NGF treated and control groups, two types of structures of the surface were recognized, smooth surfaced and rough surfaced neurons. Growth cones and varicosities of the processes were observed after 12 hours of culture in NGF-treated groups, in contrast they were observed after 24 hours in control groups. The size and number of growth cone and varicosity was greater in NGF-treated groups than in control groups. NGF elongated the processes of DRG neurons after 24 hours of culture. NGF also significantly increased the number of surviving neurons after 48-72 hours of culture. Rough surfaced neurons were more sensitive than smooth surfaced neurons to NGF in enhancing survival. These results suggest that NGF may induce maturation of DRG neurons through elongation of its processes and the formation of growth cones and varicosities. Furthermore, the perikaryal projections of DRG neurons may be related to neuron survival after NGF treatment.