We report the results of typings, for immunoglobulin G allotypes, of 5392 Native Americans from ten samples, the typings having been performed over the last 20 years. Four cultural groups are represented: the Pimans-Pima and Papago; the Puebloans-Zuni and Hopi; the Pai-Walapai; and the Athabascans-Apache and Navajo. The haplotype Gm1;21 has the highest frequency in each population while Gm1,2;21 is polymorphic in all except the Hopi. The Mongoloid marker Gm1;11,13 is found primarily in the Athabascans. The Caucasian haplotype Gm3;5,11,13 is found at polymorphic frequencies in several of the populations but its frequency is very low or absent among nonadmixed individuals. Although Nei's standard genetic distance analysis demonstrates genetic similarity at the Gm and Km loci, the heterogeneity that does exist is consistent both with what is known about the prehistory of Native Americans and traditional cultural categories. When the current Gm distributions are analyzed with respect to the three-migration hypothesis, there are three distinct Gm distributions for the postulated migrants: Gm1;21 and Gm1,2;21 for the Paleo-Indians 16,000 to 40,000 years ago; Gm1;21, Gm1,2;21, and Gm1;11,13 for the second wave of Na-Dene hunters 12,000 to 14,000 years ago; and Gm1;21 and Gm1;11,13 for the Eskimo-Aleut migration 9,000 years ago. The Pimans, Puebloans, and the Pai are descendents of the Paleo-Indians while the Apache and Navajo are the contemporary populations related to the Na-Dene. Finally, the Gm distribution in Amerindians is found to be consistent with a hypothesis of one migration of Paleo-Indians to South American, while the most likely homeland for the three ancestral populations is found to be in northeastern Asia.