Utilizing the somatic cell hybridization technique, we established 12 clones of mouse hybridoma from MRL/Mp-lpr/lpr(MRL/1) and NZB X NZW(B/W F1) mice, which produce antibodies reacting mainly with ssDNA (anti-ssDNA) and 2 clones from B/W F1 mice, which produce antibodies reacting with both ssDNA and dsDNA (anti-ss/dsDNA). By means of a competitive inhibition radioimmunoassay with synthetic polynucleotides, the anti-ssDNA antibodies were classified into 5 types, in terms of the DNA base specificity. The anti-ss/dsDNA antibodies had polyspecific reactivity to a wide range of polynucleotides, including synthetic RNA.