Locked nucleic acid (LNA) is a nucleic acid analogue that displays unprecedented hybridization affinity towards complementary DNA and RNA. Structural studies have shown LNA to be an RNA mimic, fitting seamlessly into an A-type duplex geometry. Several reports have revealed LNA as a most promising molecule for the development of oligonucleotide-based therapeutics. For example, Tat-dependent transcription and telomerase activity have been efficiently suppressed by LNA oligomers, and efficient cleavage of highly structured RNA has been achieved using LNA-modified DNAzymes ('LNAzyme'). Furthermore, convincing examples of the application of LNA to nucleic acid diagnostics have been reported, including high capturing efficiencies and unambiguous scoring of single-nucleotide polymorphisms.