The nuclei were isolated from the root meristematic cells of Allium cepa and the nuclear matrices were prepared. A 135 kD polypeptide, which is equivalent to Sc II in molecular weight, was revealed in the nuclei by SDS-PAGE and was then demonstrated to be an Sc II-like protein by Western blot with an anti-chicken Sc II antiserum. Neither the 135 kD polypeptide nor the positive labelling of the anti-Sc II antiserum was found in the nuclear matrices. The immuno-fluorescence tests showed that the nuclei labelled with the anti-Sc II antiserum emanated strong, specific fluorescence, while the fluorescence of the nuclear matrices was too weak to be detected. The results of immunoelectron microscopy indicated that a large number of the gold particles were concentrated in the condensed chromatin of the nuclei, but very few gold particles were distributed in cytoplasm and nucleoplasm. These results strongly suggested that an Sc II like protein is a component of the nuclei of A. cepa and is mainly located in the condensed chromatin regions, but the nuclear matrices contain no or very little amount of that protein. By means of immunofluorescence and immunoelectron microscopy, the chromosomes and chromosomal scaffolds of A. cepa labelled with the anti-chicken Sc II antiserum were observed to send off specific fluorescence and have many gold particles representing the presence of the Sc II-like protein distributed among them. The significance of the Sc II-like protein as a novel component in the nuclei, chromosomes and chromosome scaffolds of higher plants is discussed.