The nuclease resistance of a short, thermostable mini-hairpin, d(GCGAAGC), and other related hairpins was examined. Hairpins possessing a purine-rich (GAA) or (GAAA) loop appeared to be more resistant against nucleases than those with a pyrimidine-rich loop or single-stranded oligomers. Among 8 kinds of oligodeoxyribonucleotides examined, the fragment most resistant against nucleases was a hairpin with the sequence of d(CGCGAAGCG). This hairpin was then utilized for the stabilization of mRNA in an in vitro translation system; the 3'-terminal region of an mRNA was hybridized with an oligodeoxyribonucleotide including the sequence complementary to the 3'-terminus of the mRNA tagged with the nuclease-resistant d(CGCGAAGCG) hairpin sequence. By using this method, dihydrofolate reductase (DHFR) mRNA was stabilized against nucleases contaminating a cell-free translation system of E.coli, with a consequent increase in protein synthesis efficiency of 200%.