The results of routine antihistone antibody (AHA) assay in a preliminary series of 189 sera are presented. There were 23 positive tests (systemic lupus erythematosus, 8 cases; drug induced SLE, 4 cases; rheumatoid arthritis 7 cases; and multiple sclerosis, 1 case; chronic active hepatitis, 1 case; systemic sclerosis, 1 case and primary biliary cirrhosis 1 case). The results of routine assay in 5 other patients groups are reported: 30 spontaneous SLE (9 positive AHA), 63 rheumatoid arthritis (2 positive AHA), 19 Sjögren syndrome (no AHA), 11 primary biliary cirrhosis (1 positive AHA) and 7 mixed connective tissue disease (no AHA).