The location of a specific major polypeptide present in nuclear pore complex-enriched fractions from rat liver was examined by indirect immunofluorescence microscopy using chicken antibodies against this polypeptide. In both whole cell preparations of cultured cells grown on cover slips (mouse 3 T 3, rat kangaroo PtK2) and in frozen sections through liver and mammary gland tissue a strongly preferential, if not exclusive, binding to the nuclear periphery of interphase cells was observed. The specificity of this localization was demonstrated in these cells by the decoration of chromatin with antibodies against histones and of elements of the endoplasmic reticulum--outer mitochondrial membrane--system with antibodies to cytochrome b5. In addition, the localization was examined by electron microscopy using frozen sections and" immunoperoxidase" techniques. The results suggest that this polypeptide is contained in a protein specific for the nuclear periphery, probably closely associated with the peripheral chromatin.