The binding of antinuclear antibody-positive juvenile arthritis (JA) sera to bovine thymus histones H1, H2A, H2B, H3, and H4 was studied by an enzyme-linked immunosorbent assay. Seventy-five percent of the JA patients tested positive for at least 1 antibody specificity. Antihistone antibodies were predominantly IgM, while IgG antibodies were less common and were restricted to histones H1 or H3. In the group of patients with JA of pauciarticular onset, antihistone antibodies were significantly more elevated in patients with past or present uveitis than in patients without a history of uveitis. Anti-H1 antibodies in JA patients were found to react mostly with determinants located in the carboxyl-terminal domain of the H1 molecule. Sera were also reactive with human histone H1(0) or chicken histone H5, which are H1 variants found only in nondividing cells.