Regenerating islet-derived 3 delta (REG3D) is a member of the secreted Reg superfamily and contains one typical C-type lectin domain. Regenerating gene (Reg), first isolated from a regenerating islet cDNA library, encodes a secretory protein with a growth stimulating effect on pancreatic beta cells. Reg and Reg-related genes which were expressed in various organs have been revealed to constitute a multigene family, the Reg family, which consists of four subtypes (types I, II, III, IV) based on the primary structures of the encoded proteins of the genes, which are associated with tissue repair and have been directly implicated in pancreatic beta-cell regeneration. Reg proteins are expressed in various organs and are involved in cancers and neurodegenerative diseases. They display a typical C-type lectin-like domain but possess additional highly conserved amino acids.