The frequency distribution of plasma glucose concentrations in certain populations show two distinct sub-groups, viz. the non-diabetic group and a hyperglycaemic group. The two groups show up as a double peak (bimodality) in the best-fit frequency distributions of log plasma glucose, and the separation or cut-off point where the two curves intersect, gives an indication of the plasma glucose level at which diabetes could be diagnosed. Venous plasma glucose concentrations two hours after a 75 gm oral glucose load were determined in the Micronesian population of Nauru and the urban Polynesian population of Western Samoa, in subjects aged 20 years and over. Both communities exhibit bimodal frequency distributions of plasma glucose in the upper age groups in both sexes. In the younger age groups the frequency distribution of plasma glucose typically follows the usual unimodal Gaussian curve. However, the high prevalence Nauruans show the bimodal form in all groups except the youngest males. The data show that among these two communities, as with the Pimas, the frequency distribution of plasma glucose concentrations can be used to separate the population into normal and hyperglycaemic groups.