This review focuses attention on the expression of peripherin and the low-molecular mass neurofilament protein during development, as well as on recent results concerning the roles of these neuronal proteins. Peripherin is the only type III intermediate filament that has been shown to be expressed in neurons but exclusively in motor, sensory and sympathetic neurons; moreover, it is co-expressed with neurofilament proteins (NFP). Clearly, peripherin is expressed concomitantly with axonal growth during development, and its synthesis appears necessary to axonal regeneration in the adult. As to NFP, they are presumed to maintain the axonal diameter and thereby ensure a normal conduction velocity. In many neuropathies, either occurring in man or provoked by different means in animals, the neurofilament network is disrupted thus giving rise to bundles of filaments in perikarya or along axons; consequently, the axonal transport is impaired. The possible significance of the overexpression of NFP is discussed.