Antibodies to total histones and histone fractions H1, H2a‐H4, H2b, and H3 were measured in serum samples from 61 patients with systemic lupus erythematosus (SLE), 33 with rheumatoid arthritis, 17 with systemic sclerosis, and 20 with various other diseases by use of a sensitive immunoenzymatic assay. Histone antibodies were present in 52.4% of the SLE samples whereas only 1 of the samples from other diseases was positive (systemic sclerosis). The presence of these antibodies in SLE patients was not associated with any specific clinical manifestations, but was correlated with activity of the disease: 87% (20 of 23) of patients with active SLE, in particular 9 of 9 not yet treated, showed histone antibody whereas only 18% (4 of 22) of samples from patients with inactive SLE were positive. We believe that the measurement of histone antibodies would be a useful addition to the present laboratory parameters (antinuclear and double‐stranded DNA antibodies and circulating immune complexes) for the diagnosis and progression of systemic lupus erythematosus, particularly since they seem to appear during or just before the onset of an active phase and tend to be absent during remission.