A study of rural and periurban children aged 10-19 years in the Tolai population of Papua New Guinea has demonstrated a higher average plasma glucose concentration and relative hyperinsulinaemia after an oral glucose challenge in the periurban group. The findings could not be explained by differences in age or adiposity. In the rural children, plasma insulin concentration remained consistently low throughout the range of glucose tolerance, indicating a high degree of insulin sensitivity. In the periurban children there was a marked increase in plasma insulin concentration with increasing plasma glucose concentration, possibly suggesting the development of insulin resistance, or an antecedent state, and incipient glucose intolerance. In view of the potential public health implications of these findings, further ecological studies of insulin response in children and adolescents would appear warranted. These should include appropriate measures of pubertal development, which is a possible confounding factor not addressed in the present study, as well as addressing the role of nutritional factors.