Locked nucleic acid (LNA) is a modified RNA in which the ribose moiety is conformationally restricted by a 2’-4’-methylene bridge to adopt a C3’-endo conformation. Incorporation of LNA-nucleotides significantly increases the melting temperature of oligonucleotides. We offer LNA with phosphodiester or phosphorothioate linkages. Phosphorothioate bonds are phosphodiester analogues in which the non-bridging oxygen has been replaced by sulphur, increasing resistance against nuclease digestion.