We studied the ability of synthetic single-stranded 30-mer oligodeoxyribonucleotides (oligoDNAs) with three different kinds of hexamer palindromic sequence to induce interferon (IFN) production of human peripheral blood lymphocytes (PBL). When PBL was cultured with oligoDNA having a palindrome of AACGTT or GACGTC, IFN activity was detected by bioassay in the culture fluid after 8 h, and the amount of IFN reached the maximum after 18 h. IFN-alpha was predominantly produced, and small amounts of IFN-beta and IFN-gamma were also found. OligoDNA with the palindrome ACCGGT had no effect.