A total of 630 haplotypes for the phenylalanine hydroxylase (PAH) gene locus were established in five groups of Polynesians comprising Samoans, Tongans, Cook Islanders, Maori, and Niueans. Considerable genetic continuity was demonstrated between these widely dispersed populations, since three common haplotypes (4, 1, and 7) constituted over 95% of alleles. A control group of individuals from Southeast Asia shared the same major haplotypes, 4, 1, and 7, with Polynesians. These data provide further support for the theories of genetic homogeneity and of Asian affinities of the Polynesian precursor populations. The absence of severe phenylketonuria (PKU) in both Polynesians and Southeast Asians is consistent with the lack of PAH haplotypes 2 and 3, on which the severe PKU mutants have arisen among Caucasians.