This study aims to describe a novel antinuclear antibody directed to proteins only accessible during the mitosis: anti-“dividing cell antigen” (DCA) antibody. A total of 709 disease-associated and control sera was tested by indirect immunofluorescence using a variety of cell lines as substrate. Cells were treated with enzymes and antibodies absorbed with nuclear antigens. Antibodies to DNA, histone subfractions, and synthetic peptides were evaluated using enzyme-linked immunosorbent assays. Cell extracts were electrophoresed before and after synchronization and sera tested on the blots. The anti-DCA antibody was demonstrated in 10 of 183 SLE patients but virtually never in other connective tissue diseases. The DCA was sensitive to HCl and proteolytic enzymes and the anti-DCA binding inhibited by histones H2A and H2B. Differences of anti-H2A and anti-H2B were observed between anti-DCA antibody-positive and anti-DCA antibody-negative sera, and antibodies specific for the 1–15 region of H2A, the 1–25 region of H2B and the 1–29 region of H4 were more frequent in the former sera than in the latter. The anti-DCA antibody was shown to react with a 60-kDa protein. Our findings suggest that the anti-DCA antibody is directed to a protein complex containing H2A and H2B.