The unique combination of immunocytochemistry with embedment-free electron microscopy was applied for precise and specific localisation of BAX in the human colon adenocarcinoma COLO 205 cell line stimulated to undergo apoptosis by camptothecin (DNA topoisomerase I inhibitor). Camptothecin-induced apoptosis was associated with redistribution of BAX from cytosol to organelle membranes: mitochondria, Golgi apparatus, endoplasmic reticulum and via nuclear envelope pores to the nucleus, occurring within 60–180min of cell exposure to the drug. An increase in BAX immunoreactivity on fine filaments and the lamina-pore complex of the nuclear matrix was also observed. The increase in BAX expression in the nuclear area of camptothecin-treated COLO 205 cells was confirmed by quantitative analysis using laser scanning cytometry. The subcellular translocations of BAX preceded the appearance of any morphological symptoms of apoptosis.