The intermediate filaments (IFs) are a multigenic family of 10-nm cytoskeletal polypeptides that have been partially classified according to their cell-specific expression patterns in mammals. Since the IFs have been highly conserved during vertebrate evolution, the objective of the present study was to evaluate the immunological cross-reactivity and tissue distribution patterns of IF types I, II, and III in the common carpCyprinus carpio. A panel of six heterologous antibodies were evaluated with a streptavidin–biotin–peroxidase complex detection system. The monoclonal antibody AE3, specific for human cytokeratins 1–8 (type II IFs), stained a wide variety of epithelial and nonepithelial tissues. Staining with the AEI monoclonal antibody, specific for human cytokeratins 10, 14–16, and 19 (type 1 IFs), resulted in similar, although generally less intense, staining of all tissues relative to the AE3 antibody. However, the AE1 antibody stained myocardial and skeletal muscle fibers in contrast to the pattern achieved with the AE3 antibody. The polyclonal antibody 68–121, specific for mammalian vimentin (type III IFs), stained a variety of nonepithelial tissues that included various connective tissue cells (fibroblasts, muscle cells, and chondrocytes), glial cells, neurons, lymphohematopoietic cells, and chromatophores. The 68–121 antibody also resulted in the restricted staining of simple and stratified epithelia. In contrast, staining with the antimammalian vimentin monoclonal antibody V9 was restricted to the cells and fibers of the retinal ganglion layer, basal lamina of the integument, lens epithelium, meninx, and choroid plexus epithelium, whereas the antimammalian vimentin monoclonal antibody Vim 3B4 did not stain. Staining with the monoclonal antibody 33, specific for mammalian desmin (type III IFs), was negative except for an intense staining pattern of the ocular lens epithelium. The localization of vimentin and the cytokeratins in various epithelial and nonepithelial tissues of the common carp indicates that IF expression in teleosts is fundamentally different than that in mammals relative to cell type specificity and expression.