Three sets of mitotic chromosomes were observed in wild type or cdc mutants (nda3-KM311 and nda2-KM52) of the fission yeast S. pombe by the DAPI staining method. The block of microtubular functions by thiabendazole or by the mutations caused their individual appearance in mitotically arrested cells. The chromosomes have a characteristic size; the length ratio of short, medium and long ones was roughly 1:2:3, consistent with the previous genetical data (Kohli et al. 1977). Double staining with ethidium bromide and DAPI showed that the nucleolus was always associated with the shortest chromosome. Pair-like structures resembling sister chromatids were also seen. 