As part of ongoing studies to define the nature of anti-nuclear antibodies in autoimmune hepatitis and assess their clinical significance, we tested sera from 65 patients who had previously been screened for reactivities to recombinant ribonucleoproteins (U1RNP-A and U1RNP-70K), ribonucleoprotein complexes (52K SSA/Ro and 60K SSA/Ro) and centromere (Cenp-B) for antibodies to histones by enzyme immunoassay. Twenty-three specimens were reactive to histones (35%). Eleven of the 23 seropositive specimens were also reactive to other nuclear antigens (48%); 12 specimens (52%) were reactive only to histone. Histone-reactive sera did not have a characteristic pattern by indirect immunofluorescence. Patients with antibodies to histones were indistinguishable from other by age, gender, clinical and laboratory findings. HLA phenotype, or responses to corticosteroid therapy. Eighteen sera (28%) that had demonstrated nuclear reactivity by indirect immunofluorescence lacked reactivity to the five recombinant nuclear antigens and histones. We conclude that antibodies to histones are common in autoimmune hepatitis and that they are an important species associated with antinuclear reactivity. In some patients, they may be the only findings. Seropositive patients lack distinctive features or different outcomes after therapy. Reactivities against other nuclear antigens probably exist and remain undefined.