Peptide tyrosine tyrosine (PYY) was identified in 1980 by K Tatemoto, in extracts of porcine small intestine, as a candidate hormone, i.e. a peptide with a C-terminal amide structure. It was found to have considerable sequence similarities to a previously identified candidate hormone, pancreatic polypeptide (PP) extracted from the pancreas of birds and mammals in 1973, and was proposed as a member of a new family of biologically active agents. Working with Kazuhiko we demonstrated biological activity in 1982 and showed PYY was present in the human gut and circulation. When PYY was infused in man to mimic physiological postprandial concentrations we showed it inhibited gastric emptying (Allen et al 1984). PYY was thus established as a hormone released from mucosal endocrine cells by nutriments and which helped control digestive process. Its importance was enhanced when it was shown to inhibit food intake in man and animals and that this occurred at physiological concentrations. Since the action was direct on the CNS it established a gut brain axis, illustrating that a fundamental psychological drive, hunger, could be controlled by a peripheral hormone. Safe regulation of food intake in the treatment of obesity is an important pharmaceutical goal. We have recently been developing suitable PYY analogues to aid in this goal.