In normal weight subjects, classified by a 2-h glucose infusion test as having normal (11), borderline (3) or pathological (9) carbohydrate tolerance (CHT), subcutaneous adipose tissue was removed under intracutaneous anesthesia by surgical biopsy. The biological responsiveness of isolated adipocytes as well as adipose tissue fragments measured as incorportion of (1-14C) glucose into CO2 or triglycerides was studied in the absence or presence of different insulin concentrations. In persons with normal CHT the insulin-stimulated (62.5 microU/ml) glucose conversion to CO2 by adipocytes as well as fat pads increased significantly up to 156 +/- 14% and 285 +/- 30%, respectively. Insulin enhanced the glucose incorporation into triglycerides up to 154 +/- 20% (fat cells) and 258 +/- 30% (fat pads) in adipose tissue from subjects displaying a normal CHT. Rates of glucose oxidation and triglyceride synthesis was markedly reduced in adipose tissue obtained from patients with borderline or pathological CHT. A significant positive relationship was found between glucose oxiation to CO2 and triglyceride production of fat cells and fat pads (r = 0.964 and 0.783, respectively). There was no correlation with responsiveness of adipose tissue to insulin and insulin secretion during glucose infusion test. The results indicate that sensitivity to insulin of target cells might be important for the development of carbohydrate intolerance also in normal weight subjects.