Process extension is a most marked and characteristic neuronal feature that is observed during the development, regeneration and plasticity of nervous system tissues. Neuro-p24, a novel membranous protein with a molecular weight of 24 kDa, is specifically localized in neurons, particularly in the neurites. Based on its molecular structure and distribution pattern in the brain we proposed that Neuro-p24 plays a role in neurite extension. In the present study we have made several findings that support this hypothesis; first, Neuro-p24 was abundant in motor axonal fibers, neurites of dorsal root ganglia neurons and apical dendrites of cerebral cortex neurons when their extension or arborization was proceeding very actively. Secondly, when COS-7 epithelial cells were transfected with either wild-type or deletion-mutated Neuro-p24 cDNAs, ectopic expression of wild-type cDNA caused morphological alterations resulting in a neuron-like appearance. These observations firmly support our proposal and indicate that Neuro-p24 plays an important role in the nervous tissue.