GPT phenotype determinations were performed in 4,148 unrelated Norwegians. The frequencies of the two common alleles were Gpt1 = 0.537 and Gpt2= 0.461. A total of 13 individuals showed the phenotypic expression of 3 rare GPT alleles, Gpt3, Gpt6, and Gpt7. No heterogeneity in phenotype distribution was found, neither in the two sexes nor regionally in Norway. 97 foreigners involved in paternity cases in Norway showed a phenotype distribution not differing from that of Norwegians. In two small additional samples of Ethiopians and Easter Islanders, Gpt1 frequencies were 0.737 and 0.531, respectively. There were significant differences in phenotype distribution between Norwegians and all African populations tested, some of the Asiatic population, Lapps and a few other populations.