Enzymuria and low molecular weight proteinuria reflect tubular damage and dysfunction, respectively. We examined urinary N-acetyl-beta-D-glucosaminidase (U-NAG) and beta(2)-microglobulin (U-beta(2)M) excretion in 17 steroid-resistant and 39 steroid-sensitive children with nephrotic syndrome whose glomerular filtration rates were within the normal range. Fourteen healthy children were taken as controls. U-NAG and U-beta(2)M levels did not show a difference between the steroid-resistant and steroid-sensitive groups but were significantly higher in the nephrotic groups compared to the controls (p < 0.0001 and p < 0.01, respectively). In the steroid-sensitive group, U-NAG levels were significantly higher in patients in the relapse phase than in those in remission (p < 0.0001). This finding was also valid for U-beta(2)M excretion, but reached significance only for patients in remission who did not receive steroids (p < 0.01). There was a positive correlation between proteinuria and U-NAG and U-beta(2)M excretion in all patients (r(s) = 0.69, p < 0.001 and r(s) = 0.39, p < 0.001, respectively). In conclusion, massive glomerular proteinuria may cause a marked U-NAG excretion and a moderate urinary U-beta(2)M elevation independent of primary renal disease.