The classification of peptidases into clans and families was first published in 1993 (20) , and this was converted into an Internet resource, the MEROPS database (21), in 1996. The database was extended to include nomenclature and bibliographies, and has been developed over the years to be a one-stop shop for researchers with an interest in proteolysis. The collection of known cleavages in substrates which was started in 1998 (22) has now been added to the MEROPS database. For each peptidase there is a page listing known substrates, and, where enough substrates are known, the peptidase summary has displays to show peptidase specificity. For each protein substrate, the sequence is displayed showing where cleavage occurs and which peptidase performs that cleavage. In addition to the MEROPS collection, there is also a collection of physiologically relevant protein cleavages assembled by the CutDB database (23) and more specialist collections of substrates for individual peptidases or peptidase families, such as CASBAH for caspases (24) .