A diabetes survey was conducted in the highlands of Papua New Guinea in June 1983. Two villages in the Asaro Valley, Eastern Highlands Province, were selected for study. The subjects were of Melanesian ancestry, and were free of Austronesian genetic admixture. The response rate was 95% and 308 subjects were examined. As defined by current WHO criteria, there was a total absence of non-insulin-dependent diabetes (NIDDM) in these communities. The prevalence of impaired glucose tolerance (IGT) was 2%. These estimates of glucose intolerance are the lowest yet to be reported from the Pacific, using currently accepted diagnostic criteria and standardized survey methods. The 2-hr plasma glucose and insulin concentrations were positively correlated in both sexes. Of the two villages studied, one had undergone a greater degree of acculturation than the other. Both the total distribution and the mean value of 2-hr plasma glucose concentration were lower in the more traditional village, and these findings could not be explained by differences in age or obesity between the two communities. Mean 2-hr plasma insulin concentration did not differ significantly between the two villages, and was very low in both. The results of this study support the theory that Melanesians free of Austronesian genetic admixture are relatively, though not absolutely resistant to the deleterious influence of acculturation upon glucose tolerance seen in other Pacific populations. However, the notion that in this population cultural change has been insufficient, or of too recent onset for a deterioration in glucose tolerance to be manifest cannot be excluded.