We have characterized the nuclear matrix-intermediate filament fraction from control and apoptotic HL-60 cells. Apoptosis was induced by exposure to the topoisomerase I inhibitor, camptothecin. By means of two-dimensional polyacrylamide gel electrophoresis, striking qualitative and quantitative differences were seen in the protein composition of the nuclear matrix-intermediate filament fraction obtained from apoptotic cells in comparison with controls. Western blotting analysis of apoptotic nuclear matrix proteins revealed degradation of some (topoisomerase IIalpha, SAF-A) but not other (SATB1 and nucleolin) components. Moreover, immunofluorescent staining for typical matrix antigens (NuMA protein, lamin B, SC-35) showed that in 35-40% of the structures prepared from apoptotic samples, marked changes in the subnuclear distribution of these proteins were present. Striking morphological differences between control and apoptotic samples were also detected at the ultrastructural level. These results demonstrate that both biochemical and morphological changes can be detected in the nuclear matrix prepared from apoptotic HL-60 cells.