There have been very few developments that markedly affect the need to greatly revise the text from the last version of this book. This is testament to the fact that hetero- neous enzyme-linked immunosorbent assays (ELISA) provide ideal systems for dealing with a wide range of studies in many biological areas. The main reason for this success is test flexibility, whereby reactants can be used in different combinations, either attached passively to a solid phase support or in the liquid phase. The exploitation of the ELISA has been increased through continued development of specifically...