Population-based data on 1,842 subjects from six semitraditional Pacific communities, collected in the years 1978-1983, have been compared in order to examine the hypotheses that differences in the distribution of plasma glucose concentration between populations are to some extent genetically determined, and that non-Austronesian (NAN) Melanesians are relatively resistant to glucose intolerance. Semitraditional communities were chosen for study so that the comparison would be minimally confounded by either known or as yet undetermined environmental factors associated with nontraditional living, the effects of which may vary between populations. The samples were also selected so as to provide a gradient of proportional NAN and AN admixture. They were drawn from the following regions: the highlands of Papua New Guinea, New Caledonia, Fiji, the Wallis Islands, Western Samoa, and Kiribati (formerly the Gilbert Islands). The Papua New Guinea highlanders, of entirely NAN ancestry, were regarded as the baseline population. A gradient of increasing mean 2-hr plasma glucose concentration was observed across the six populations and differences persisted between populations, after controlling for age and obesity. Variations in diet, physical activity, and degree of sociocultural modernization were not considered a sufficient or consistent explanation of these findings and they therefore lend tentative support to the hypothesis of a genetic component to variability in glucose tolerance. The relationship between population estimates of glucose tolerance and estimates of the genetic distance from the baseline NAN Melanesian sample was examined. With the notable exception of Fiji, there was evidence of a linear correlation between the two parameters.