While frequency distributions of glucose concentrations in Caucasian populations are unimodal, bimodality has been described in the Pima Indians, a population with an extremely high prevalence of diabetes. Venous plasma glucose concentrations at fasting and after a 75-gm. oral glucose load were determined in 596 Nauruans, a Micronesian population with a diabetes prevalence of the same order as the Pima Indians. In both sexes and in subjects 10 to 19 years, the frequency distributions of the logarithms of the fasting and two-hour glucose values were clearly unimodal. In most sex and age groups of 20 years and older, the frequency distributions of fasting and two-hour glucose values were bimodal and consistent with a model of two overlapping Gaussian distributions. This population is characterized by marked obesity. However, there was no significant difference in the degree of obesity between subjects in the first and second curves of the bimodal distribution. This makes it unlikely that the bimodality is a consequence of the marked obesity seen in both the Pima and Nauru populations. The data show that among Nauruans, as with the Pimas, the frequency distribution of glucose concentrations can be used to separate the population into normal and hyperglycemic groups.