Peptide nucleic acid (PNA) is a nucleobase oligomer in which the entire backbone has been replaced by a backbone composed of N-(2-aminoethyl)glycine units. In other words, PNA can be regarded as DNA with a neutral peptide backbone instead of a negatively charged sugar-phosphate backbone. It is chemically stable and resistant to hydrolytic (enzymatic) cleavage and thus not expected to be degraded inside a living cell, although its transportation within the cell is difficult. PNA is capable of recognising specific sequences of DNA and RNA obeying the Watson-Crick hydrogen bonding scheme, and the hybrid complexes exhibit extraordinary thermal stability and unique ionic strength effects. It may also recognise duplex homopurine sequences of DNA to which it binds by strand invasion, forming a stable PNA/DNA/PNA triplex with a looped-out DNA strand. PNA exhibits superior hybridisation characteristics and improved chemical and enzymatic stability relative to nucleic acids, which is why PNA finds major applications in the diagnostic and pharmaceutical fields. Studies indicate that PNA is capable of inhibiting transcription as well as translation, so it can be used as a new tool for antigene and antisense therapy. Owing to its superior properties, PNA could replace DNA as a probe for many investigation purposes. This paper reviews the synthesis of PNA, its important properties making it a new hot tool in the market and its major applications. (c) 2006 Society of Chemical Industry.