Microalbuminuria has been reported to precede the development of NIDDM and to be a risk marker for cardiovascular disease. Therefore, the present study investigated the relationship between urinary albumin excretion rate (UAER) and the degree of insulin resistance in Japanese subjects with impaired glucose tolerance (IGT). Thirty-three normotensive IGT subjects were divided into three groups and twenty hypertensive IGT subjects were divided into two groups according to the degree of insulin resistance (GIR value) estimated by the euglycemic hyperinsulinemic clamp method. UAER was significantly higher in the lower GIR group in normotensive subjects (highest GIR group, 6.6 +/- 0.9 mg/24 h; intermediate group, 10.5 +/- 3.0 mg/24 h; lowest group, 21.3 +/- 3.8 mg/24 h; P<0.01 between highest and both of the other groups), but not in hypertensive subjects. The lowest GIR was associated with higher fasting plasma insulin, increased insulin response to glucose, higher plasma triglyceride and uric acid, and lower high-density-lipoprotein cholesterol, but not with increased creatinine clearance rate in normotensive subjects. A similar tendency was also found in hypertensive subjects. It is concluded that UAER is related to insulin resistance in normotensive subjects with IGT through a mechanism other than glomerular hyperfiltration.