p330d/CENP-F is a novel proliferation-associated and cell cycle-dependent centromere autoantigen which appears to play a very important role in mitotic progression. As an initial step in exploring the clinical and biological significance of autoantibodies to this protein, we evaluated the clinical histories of 26 patients producing these antibodies. The antibodies were detected by both indirect immunofluorescence microscopy (IIF) and Western blotting. All the sera contained anti-p330d/CENP-F IgG antibodies, with an average titer by IIF of 1:6,917 (range 1:160 to 1:20,480). Most of the patients had disorders associated with abnormal or increased cell proliferation at the time the anti-p330d/CENP-F antibodies were detected. These included cancers of various types (14), chronic liver disease (3), chronic rejection of renal allografts (2), and Crohn's disease (1). The average IIF titer of the anti-p330d/CENP-F antibodies in the patients with cancer, 1:10,103, was significantly higher than the average titer in non-cancer patients, 1:3,200 (P = 0.008). Autoimmunity to p330d/CENP-F appeared not to be associated with rheumatic diseases, in particular scleroderma, since only three of the 26 patients had rheumatic disease and the antibodies were not detected by IIF in a group of 351 patients with scleroderma and related disorders. Our findings, although retrospective and limited to a relatively small number of patients, point to the hypothesis that autoimmunity to p330d/CENP-F could be related to events involving increased or abnormal cell proliferation.