Regenerating gene (Reg), first isolated from a regenerating islet cDNA library, encodes a secretory protein with a growth stimulating effect on pancreatic beta cells that ameliorates the diabetes of 90% depancreatized rats and non-obese diabetic mice. Reg and Reg-related genes 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 [Diabetes 51(Suppl. 3) (2002) S462]. Plural type III Reg genes were found in mouse and rat. On the other hand, only one type III REG gene, HIP/PAP (gene expressed in hepatocellular carcinoma-intestine-pancreas/gene encoding pancreatitis-associated protein), was found in human. In the present study, we found a novel human type III REG gene, REG III. This gene is divided into six exons spanning about 3 kilobase pairs (kb), and encodes a 175 amino acid (aa) protein with 85% homology with HIP/PAP. REG III was expressed predominantly in pancreas and testis, but not in small intestine, whereas HIP/PAP was expressed strongly in pancreas and small intestine. IL-6 responsive elements existed in the 5'-upstream region of the human REG III gene indicating that the human REG III gene might be induced during acute pancreatitis. All the human REG family genes identified so far (REG Ialpha, REG Ibeta, HIP/PAP, REG III and REG IV) have a common gene structure with 6 exons and 5 introns, and encode homologous 158-175-aa secretory proteins. By database searching and PCR analysis using a yeast artificial chromosome clone, the human REG family genes on chromosome 2, except for REG IV on chromosome 1, were mapped to a contiguous 140 kb region of the human chromosome 2p12. The gene order from centromere to telomere was 5' HIP/PAP 3'-5' RS 3'-3' REG Ialpha 5'-5' REG Ibeta 3'-3' REG III 5'. These results suggest that the human REG gene family is constituted from an ancestor gene by gene duplication and forms a gene cluster on the region.