Use of an immunoenzyme technique to seek two types of antibody (AB): antihistones and bicatenary anti-RNA, led to study of their distribution in different connective tissue and autoimmune diseases. Total antihistone AB and the H1 and H2b antifractions were seen almost exclusively in lupus (52.5 per cent of cases), principally during active phases of the disease since 87 per cent of active forms had antihistone AB as against 15 per cent of inactive forms. Antihistone AB would thus appear to be a valuable laboratory investigation in the diagnosis and surveillance of lupus. Bicatenary anti-RNA AB were more widely distributed, being found in DLE, RA, scleroderma and in various disorders with antinuclear antibodies. However they were slightly more common in active forms of lupus and their titres appeared to fall more quickly than those of antinuclear AB and anti-DNA AB at the time of clinical improvements. In RA, bicatenary anti-RNA AB were more commonly associated with inflammatory and progressive forms but further studies involving larger populations would be necessary to confirm these findings.