We have investigated plasma glucose and immunoreactive insulin responses to 75-g oral glucose in lean, young, full-blood Aboriginal men from urban and rural communities and made comparisons with age- and weight-matched Caucasoids. Fasting glucose concentrations were lower in the rural Aborigines than in the urban Aborigines or the Caucasoids. Plasma glucose concentrations 2 h postprandially were significantly higher in both Aboriginal groups (urban 6.7 +/- 0.6 mmol/l, rural 6.4 +/- 0.4 mmol/l) than in the Caucasoids (5.0 +/- 0.3 mmol/l). Insulin responses in the two Aboriginal groups were almost identical and 50% higher than in the Caucasoids. We also investigated glucose tolerance and plasma lipids in 67 full-blood Aborigines living in an isolated rural community. Only three people (two men and one woman) had diabetes while a further eight (six men and two women) had impaired glucose tolerance. Fasting plasma cholesterol concentrations did not increase with age and were significantly lower in the rural Aboriginal community than in either the urban Aborigines or the Caucasoids. These results suggest that elevations in fasting cholesterol and glucose concentrations are lifestyle-associated, but that mild impairment of glucose tolerance and high insulin response in the Aborigines may be inherited metabolic characteristics.