We have applied monoclonal antibodies generated against nuclear matrix in an immunofluorescence study of a variety of plant and animal species. Antibodies P1 and I1 detected antigens in all species examined, including higher and lower plants. Antibodies PI1 and PI2 stained only animal cells, and showed some tissue and/or species-specific variability in staining pattern. The presence of similar nuclear matrix components in such diverse species suggests that nuclear order may be maintained by similar mechanisms in all eukaryotes.