A cDNA (199E) specific for the 57 kd neural IF protein has been isolated from a PC12 cell lambda gt11 library. Antibody eluted from the fusion protein produced by 199E recognizes the 57 kd protein on immunoblots and, in PC12 cells, labels a pattern of fibrillar structures identical to that seen with 57 kd antiserum. In situ hybridization using antisense RNA transcripts labels areas of the nervous system known to contain the 57 kd protein. 199E hybridizes with a single mRNA species of approximately 2.0 kb from PC12 cells. A 199E-reactive message can be detected as early as E10 in rat embryos. Southern analyses suggest that there is only one gene for this protein. Amino acid sequence predicted from 199E indicates that the 57 kd protein is a type III IF protein like vimentin and desmin. Thus, expression of IF structural genes in neurons is not limited to the type IV neuronal IF triplet proteins.