Antibodies to histone, a protein associated with DNA in the nucleus of eukaryotic cells, occur in a number of clinical conditions, primarily in systemic lupus erythematosus (SLE), drug induced LE. Histone antibodies of IgG and IgM are found in approximately 50% of unselected SLE and in 83% of active SLE patients. Almost all patients with drug induced LE and 22% of patients on certain drugs and positive for ANA have antibodies to histone.