The intracellular organization of dinoflagellate protists, particularly the cytoskeleton, the cell cycle and mitosis (“dinomitosis”), presents peculiar features governed by specific proteins. We have previously biochemically isolated and characterized a protein of 72 kDa (P72) conserved from dinoflagellates to humans. The microsequencing of the NH2-terminal sequence and the reaction with a monoclonal antibody suggested that this protein belongs to the HSP70 chaperone family (Perret et al. 1991, 1995). Using a polyclonal antibody raised against P72, we have immunolocalized this protein using standard fluorescence microscopy on cryosections, confocal laser scanning microscopy on whole mounted cells and transmission electron microscopy after fast-freeze preparation with or without high pressure during freezing. We have localized P72 in specific dense aggregates at the cortical and centrosome level, in the cytoplasmic channels passing through the nucleus during mitosis and in the cleavage furrow. We completed this study by double labelling with anti-P72/anti-β-tubulin to analyse relationships between P72 and the cytoskeleton and to discuss the possible function of P72.