Abstract. We have examined the impact of race and positive family history of type 2 diabetes on glucose/insulin dynamics and the two components of glucose disposal in healthy, first-degree relatives of black and white American patients with type 2 diabetes mellitus who are at a greater risk from the disease and their healthy control subjects. Seventeen black and 15 white relatives were studied. Twenty-two black people and 24 white people, without family history of type 2 diabetes, served as healthy control subjects. Standard oral glucose tolerance test (OGTT) and tolbutamide-modified frequent sampling intravenous glucose tolerance (FSIGT) tests were performed in each subject. Insulin sensitivity index (SI) and glucose effectiveness (SG) were calculated using the MINI-MOD method described by Bergman et al. Mean fasting and post-stimulation serum glucose levels were not significantly different in the black and white relatives. However, mean serum insulin responses to oral and/or intravenous stimulation were significantly greater in the blacks than whites, irrespective of positive family history of diabetes. The mean SI was significantly (P < 0·02) lower (52%) in the black (3·67±0·56) than the white [7·50±1·93 times 10-4 min-1 (mUl)-1] relatives. Comparing the healthy controls, the mean SI was significantly (P < 0·02) lower (51%) in black than white controls (4·84±0·78 vs. 9·71±1·27 times 10min-1(mUl)-1]. Mean SG and KG were greater (P < ·05) in the blacks than whites, irrespective of family history of diabetes. In summary, the present study demonstrates that non-diabetic black people manifest insulin resistant and hyperinsulinaemia, irrespective of family history of diabetes, when compared to white people. We speculate that these metabolic changes could play a potential role in the higher prevalence of type 2 diabetes in the black Americans.