Defensins are a large family of polypeptides occuring in most animals and plants. Since the first description of a defensin in 1985, the members of this peptide class are considered to play an important role in the innate immune defence of organisms, protecting against invading pathogens by killing bacteria and other microbes. In mammals, defensins display a broad functional spectrum, linking them to the adaptive immune system and other functions, and their expression is altered in certain disease states. This review summarises the patents that are associated with defensin peptides and their use as published between 2003 and March 2006.