The authors evaluated the significance of beta cell function, non-insulin-dependent glucose disposal (glucose effectiveness [Sg]), and insulin-dependent glucose disposal (insulin sensitivity) in African immigrants with varying degrees of glucose tolerance. Thirty-two African immigrants residing in Franklin County, Ohio, were studied. There were 16 subjects with normal glucose tolerance (NGT), 11 with intermediate glucose tolerance (IGT), and 5 with type II diabetes mellitus (DM). Insulin sensitivity index and Sg were measured by an insulin-modified, frequently sampled intravenous glucose tolerance test. The mean fasting and post-glucose serum glucose levels were lowest in the NGT, intermediate in the IGT group, and highest in the DM group. Mean serum insulin and c-peptide responses rose briskly by threefold to a peak in the NGT and the IGT groups. In the DM group, mean serum insulin and c-peptide responses were severely blunted to glucose stimulation. The sensitivity index was highest in the NGT (3.09 +/- 0.27), intermediate in the IGT (1.81 +/- 0.47), and lowest in the DM (0.48 +/- 0.28 x 10(-2).mins-1 (microU/ml)-1). The Sg was identical in the NGT (2.78 +/- 0.22) and IGT (2.78 +/- 0.27) groups but was slightly but not significantly lower in the DM (2.20 +/- 0.35 x 10(-2).mins-1). In addition, the glucose decay constant was not statistically different in the NGT (3.00 +/- 0.38) and IGT (2.25 +/- 0.19) group, but the mean values were significantly greater than in the patients with diabetes (0.78 +/- 0.15 percent/mins). The mean disposition index (sensitivity index X beta cell function as assessed by both insulin and c-peptide) was significantly greater in NGT than in the IGT (P<0.05) and in the diabetic group (P<0.001). In summary, the authors demonstrate that, in native African immigrants, type II diabetes is associated with significant reduction in beta cell function, insulin sensitivity, and glucose decay constant, but not in Sg. In patients with intermediate or impaired glucose tolerance, there is moderate insulin resistance and evidence of inadequate compensation by beta cell, but the Sg, the Sg at theoretical insulin concentration, and glucose decay constant remain normal. They conclude that, unlike other ethnic and racial groups, in glucose intolerant native African patients, alterations in Sg or non-insulin dependent glucose disposal (ie, tissue glucose sensitivity) do not appear to play a significant role in the impairment of glucose tolerance and type II diabetes in African immigrants.