The frequency distribution of log plasma glucose concentrations in certain populations show two distinct subgroups--a non-diabetic group and a hyperglycaemic group--when suitable methods of distributional analysis are used. These 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 2 hr after a 75 g oral glucose load were determined in the urban Polynesian population of Western Samoa, in subjects aged 20 yr and over. Bimodality was evident in subjects over 35 yr of age in both sexes, but for the younger age groups the frequency distribution of log plasma glucose follows the usual unimodal Gaussian curve. The data show that among these Polynesians, as with Pimas and Nauruans, the frequency distribution of log plasma glucose concentrations can be used to separate the population into normal and hyperglycaemic groups.