Progress in molecular technology in recent years has caused an amazing growth of information about intercellular peptide messengers and their receptors. The number of characterized interleukins for example numbered just three six years ago and now there are at least 16. In addition, the number of described neutrophic peptides is around 30 and the number of receptors is ever increasing. Because many of these new peptide ligands and receptors were identified by "reverse genetic" techniques the understanding of their biological roles falls behind the knowledge of their molecular structures....