The amino acid sequences of vasoactive intestinal peptide (VIP) and pituitary adenylate cyclase-activating peptide (PACAP) are given, demonstrating the high degree of homology shared by the peptides. Both VIP and PACAP bind VPAC1, VPAC2, and PAC1 receptors, initiating a signaling pathway which is transduced by the s subunit of the G protein complex (Gs), and Gs then stimulates adenylate cyclase (AC). Some of the putative functions of each receptor are also summarized.