It is suggested that the cytotoxicity of anticancer agent mitoxantrone (MITOX) is related to a complex combination of molecular interactions which lead to slowing of S phase traverse and arresting of cells in G2 phase of the cell cycle or even to an apoptosis at high concentration of MITOX. Here intracellular molecular interactions of MITOX were visualised and studied using the confocal spectral imaging technique in synchronised K562 cells. Localisation, quantitative distributions of MITOX in the polar environment, MITOX bound to hydrophobic cellular structures (MITOXphob), nucleic acid-related complexes of MITOX (MITOXNA) and relative distributions of naphthoquinoxaline (NQX) metabolite and intrinsic cellular fluorescence of porphyrins were measured within cytoplasmic and nuclear compartments (chromosomes) of the G2, S, and M cells treated with 10 or 2 microM of MITOX for 1 hour. Colocalisation of MITOX, NQX metabolite and sites of intrinsic cellular fluorescence indicates an accumulation of MITOX within or near mitochondria. One may suppose that due to high concentration MITOX can compete with natural substrates for binding to the enzymes thus affecting the normal functioning of a mitochondria. A remarkable redistribution of MITOX and its complexes occurs in the M cells. In particular, a prominent amount of MITOX is associated with the surface of chromatids but not with the cytoplasmic structures in M cells. At the present time the exact location of the sites of MITOX accumulation in the M cells is not known. It is thought to be some cytoskeleton/microtubule structures associated directly with the chromosomes. Selective labelling of particular cytoskeleton structures and/or proteins in MITOX treated cells is in the progress now and the question will be addressed using the CSI technique.