O-47 A worldwide natural clustering of HTLV-I/II would have been modified by a modern human migration with unique cultural conditions. Based on review of strict confirmatory assays on HTLV-I/II antibodies among native Mongoloid people in Pan-Pacific areas, HTLV-I is mainly detected among southwestern Japanese and Andean, including Colombian, Peruvian, Bolivian, Chilean and Argentinean, but HTLV-II is broadly spread among native people throughout the Central and South America, including Panama, Colombia, Venezuela, Brazil, Paraguay, Argentina and Chile. Furthermore, a different subtype of HTLV-I is clustered among Australoids (native Melanesians) in Oceania, including Papua New Guinea, North Australia and neighboring islands, but it is never clustered among Polynesians. An origin of HTLV-I/II among Mongoloids and Australoids is not well understood, but is probably linked to a history of human dispersal, and a geographical clustering is strongly associated with a putatively high mother-to-child and man-to-woman transmission of the virus under natural condition of each group. To investigate a unique distribution of HTLV-I among Japanese in Asia and Andean in South America, comprehensive information on immunogenetic variation among native people in Pan Pacific areas may give a hint to disclose a relationship between Japanese and Andean ancestors. The most recent genetic studies on Andean mummies could provide an explanatory evidence on migration history of Asian Mongoloid.