The lecturer recalls the discovery of glucagon receptors in liver cell membranes, the role of the adenylate cyclase-AMPc system, until recent attempts at purification and isolation of this receptor. He then reviews successively, the problems of estimation, specificity of the interaction, the effects of purine and pyrimidine nucleotides on glucagon receptor interaction, etc. The importance of the two nucleotides GTP and ATP in activation of adenylate cyclase is emphasized. The VIP receptors ("vasoactive intestinal peptide") and secretin receptors are also discussed. In some ways, they resemble glucagon receptors. The possible consequences of these discoveries arethen discussed.