During the past two decades there have been rapid advances in our knowledge of the structure and function of the protein hormones in the brain and gastroenteropancreatic system (GEP). Many published articles have highlighted the superfamily of hormonal peptides, specifically, the mechanisms and control of peptide synthesis in neural and non-neural tissues, and gene structure. Here we present an analysis of the annual trends, between 1980 and 1997, of research emphasis on six protein/peptide hormones, as reflected by their individual frequency of publication per year. Although this symposium is focused on the GEP hormones, we provide herein a perspective on the level of research activity of the hormones insulin, glucagon, cholecystokinin, insulin-like growth factor-I and -II, neuropeptide Y and somatostatin in the brain/gut systems throughout the vertebrates and invertebrates. Many publications deal with the evolution of these peptides and their superfamilies, yet as noted in this review, there are relatively few references to these peptides in invertebrates and non-mammalian species. Typically in invertebrates, the number of citations is low and mostly focused on three phyla, the arthropods, mollusks and helminths. Generally, in the vertebrates the smallest number of citations is in the cyclostomes and elasmobranchs. Because most groups of invertebrates and vertebrates have received scant attention, phylogenetic comparisons are limited. Evolutionary information concerning important groups of animals, such as helminths, mollusks, protochordates and cyclostomes, is essential to establish the phylogenetic histories of the hormonal peptides. The challenge to comparative endocrinologists is to examine species in key evolutionary positions in order to gain an understanding of the diversity and function of the hormones and to determine the molecular features that form clues to their phyletic interrelationships and progression.