Two distinct types of cell death have been described: apoptosis and necrosis. However, it is becoming increasingly clear that the differences between these two types are far less numerous than initially thought. Morphological analyses might provide important information to distinguish apoptotic from necrotic samples. We recently reported that in necrotic, but not apoptotic, HL-60 human myeloid leukaemia cells, the nuclear protein topoisomerase II concentrated in nucleoli. In order to ascertain whether or not this phenomenon was restricted to a peculiar cell type or could be detected also in cells of lymphoid lineage, we performed an investigation aimed at defining the localization of topoisomerase II in apoptotic and necrotic Jurkat human T lymphoblastoid cells. Immunofluorescence staining demonstrated that topoisomerase II was excluded from the condensed chromatin of apoptotic cells, whereas in necrotic cells it was localized in discrete nuclear dots. Immuno-electron microscopy analysis showed that topoisomerase II was undetectable in nucleoli of normal and apoptotic cells, whereas it was present in the nucleolus of necrotic cells irrespectively of the type of inducer used (ethanol, H2O2, HgCl2). Taken together, our findings identify topoisomerase II as a potential morphological marker useful to discriminate between apoptotic and necrotic cells.