Microalbuminuria is a risk factor for renal and cardiovascular disease. A role for insulin resistance in the pathogenesis of microalbuminuria has been suggested but is still unproven. In this case-control, cross-sectional study, we compared glucose disposal rate (GDR), measured by hyperinsulinemic-euglycemic clamp, in 50 pairs of matched type 2 diabetic patients with micro- or normoalbuminuria (main study) and in 29 matched pairs of diabetic patients with macro- or microalbuminuria (substudy). In the main study, GDR was approximately 25% lower in micro- than in normoalbuminuric patients (5.20 +/- 1.91 vs. 6.86 +/- 2.88 mg . kg(-1) . min(-1), P < 0.05) and was independently associated with microalbuminuria (P = 0.002), with each 1 mg . kg(-1) . min(-1) decrease predicting approximately 40% increased prevalence (odds ratio 1.37 [95% CI 1.14-1.70]). Microalbuminuria was threefold more frequent in patients with GDR < or =7.50 +/- 2.56 mg . kg(-1) . min(-1) than in those with higher GDR (60% vs. 20%, P < 0.005). In the substudy, GDR in macro- and microalbuminuric patients was comparable (5.52 +/- 2.56 vs. 5.16 +/- 1.61 mg . kg(-1) . min(-1)) and independent of macroalbuminuria. GDR was significantly correlated with urinary albumin excretion rate in the main study (P = 0.004) but not in the substudy (P = 0.60). In type 2 diabetes, more severe insulin resistance is independently associated with microalbuminuria. Longitudinal studies are needed to clarify the role of insulin resistance in the pathogenesis of microalbuminuria and related complications.