Summary The technique of counterimmunoelectrophoresis (CIE) has been adapted for detection of serum precipitins to calf thymus (CT) DNA in patients with SLE, discoid LE, miscellaneous connective tissue and infectious diseases, and control populations. Of seventy‐eight LE patients, 58% demonstrated anti‐ss DNA precipitins, and 20% exhibited anti‐ds DNA precipitins. Good correlation was noted between the presence of ss DNA precipitins and ss DNA binding values determined by the more sensitive ammonium sulphate precipitation assay. Depressed total serum haemolytic complement activity in CH50 u/ml was noted in 64% of sera exhibiting ss DNA precipitins and 38% of those with negative ss DNA precipitins. There was a strong association, however, between ds DNA precipitins and depressed serum complement levels. Although less sensitive than primary binding assays, CIE can be used as a rapid and simple screening test for detection of circulating anti‐native and denatured CT DNA precipitins. CT DNA serum precipitins are present in a significantly higher percentage of SLE patients when compared with other disease states and normal control populations.