Glucose intolerance which is frequently found in patients with the idiopathic nephrotic syndrome (INS) may be linked to an increased cardiovascular risk in these patients. Recently it has been suggested that proteinuria and steroid treatment may independently affect insulin sensitivity. The aim of the study was to assess insulin resistance (IR) and beta-cell function in children with INS at various stages of the disease. The study group comprised 66 children (32 male, 34 female; age 8.1 +/- 5.0 years). 20 healthy, sex- and age-matched subjects served as controls. The study group was divided into 3 subgroups: A (n=24) children in relapse of INS (steroids 60 mg/m2/48h; proteinuria 1.02 +/- 1.04 g/dl); B (n=20) in remission treated with steroids (30 mg/ m2/48h); C (n=22) in remission but without steroids. Fasting glucose and insulin levels were measured to calculate insulin resistance (HOMA-IR) and beta-cell function (HOMA-beta) using Homeostatic Model Assessment. Fasting glucose was within normal range in all subjects. HOMA-IR was significantly higher in group A (3.2 +/- 3.3) and group B (2.4 +/- 1.7) than in group C (1.45 +/- 1.6 and controls (1.12 +/- 0.6) (p<0.05). HOMA-beta was significantly higher in group A and B than in C and controls (p<0.05). In multivariate analysis HOMA-IR correlated with proteinuria (beta=0.45, p<0.001), steroid dose (beta=0.32) and BMI (beta=0.42). In conclusion, an increase in insulin resistance with compensatory enhanced beta-cell secretion is a typical finding in children with INS treated with steroids. Proteinuria seems to be an independent risk factor for decreased insulin sensitivity.