In an attempt to raise a set of monoclonal antibody (MAb) probes for the study of biology and diagnostic value of human keratin No. 8, a series of hybridomas was prepared and their characteristics investigated by immunohistochemistry and immunoblotting. The polypeptide specificities of individual MAbs ranged from monospecificity for keratin No. 8 (MAbs C-15, C-23, C-36, C-43, C-47, C-51, and C-61) up to the "pan-keratin" MAbs C-11 and C-66 recognizing a broad range of keratins. The target epitopes of the remaining 4 MAbs (C-10, C-22, C-50, C-69) appear to be shared by various pairs of keratin polypeptides. The immunohistochemical investigation of tissues and/or cultured cells from 10 animal species revealed considerable variability of the interspecies crossreactivity of individual MAbs. The target epitopes of 5 MAbs appear to be phyllogenetically conserved from man to Xenopus, 6 of 12 MAbs tested show reactivity with several mammalian species (but not chicken or Xenopus) and the MAb C-15 reacts with human and sheep keratin only. The data obtained demonstrate that at least 9, and possibly as many as 12, nonidentical epitopes of the human keratin 8 polypeptide can be distinguished by this set of antibodies. The results of the present study suggest that our MAbs represent a significant contribution to the list of reagents applicable in both research of intermediate filament (IF) biology and diagnostic histopathology.