Glicentin is a 69-amino-acid peptide containing glucagon and oxyntomodulin sequences in the molecule. It is suggested that glicentin and oxyntomodulin are produced in the intestinal L-cells and glucagon in A-cells in the pancreas, these peptides are derived from a common precursor by two different tissue-specific processing pathways. In 1983, the amino acid sequence of human glicentin was deduced by Bell et al. from the genomic sequence of human preproglucagon. Glicentin is a major form of gut glucagon-like immunoreactants (Gut GLIs). In mammalian small intestine, proglucagon is processed into glicentin, oxyntomodulin, and glucagon -like peptide 1(GLP-1) and glucagon -like peptide 2 (GLP-2). GLP-1(7–37) and GLP-1(7–36)amide have been isolated from the intestine and pancreas. It has been known that the GLP-1 sequence is well conserved between species in all mammals studied. Using synthetic peptides, several investigators have demonstrated that in contrast to GLP-1 (1–37), truncated GLP-1(7–36)amide and GLP-1(7–37) have several physiological effects. However, the physiological role of glicentin, a major gut glucagon, is still unclear. It has been known that the circulating level of plasma glicentin-like peptides increases significantly nutrient ingestion. Yanaihara institute Inc. has succeeded in developing a specific and convenient EIA kit for determination of rat glicentin in plasma.