Neuronal intermediate filaments are fast becoming well characterized at the molecular level. What they actually do in neurons and how they do it, however, are less clear. Their restricted cellular localization indicates that certain of their functions are uniquely neuronal. On the other hand, some basic features of neurofilament subunit structure are conserved among the various members of the intermediate filament protein family, suggesting that general principles of intermediate filament organization and dynamics may also apply to neurofilaments. New information from many laboratories now seems to be bearing out both of these predictions. A case in point is the newly discovered ability of certain class I11 intermediate filaments, vimentin and desmin, to assemble and disassemble reversibly and to reorganize rapidly as cells move and change shape [Skalli and Goldman, 199 11. These discoveries have been leading some investigators to reconsider whether we may be overlooking a more dynamic side of neurofilaments-structures that have usually been considered to be irreversible polymers. In this review, we focus on what features of class I11 filaments dynamics and regulation apply to neurofilaments. Second, we consider how specializations of polypeptide structure and posttranslational modifications unique to neurofilaments may have evolved to stabilize the filament network and to serve better the purposes of the highly polar, postmitotic neuron. Some aspects of these themes have been reviewed recently [Julien and Grosveld, 1991; Nixon, 1991; Nixon and Sihag, 1991; Shaw, 1991; Skalli and Goldman, 1991; Steinert and Roop, 19881.