We studied the relationship between the urinary microtransferrin (TRF) and early glomerular damage in diabetes mellitus. 61 patients with non-insulin-dependent diabetes mellitus and 40 healthy subjects were measured for urinary TRF with rate immunonephelometry assay. The Urinary TRF concentrations were found to be greatly elevated in patients with diabetes compared with those in the health subjects (P < 0.001). The increase of TRF was closely related to age and duration of diabetes mellitus, blood glucose, hypertension, retinopathy, and it was initial parameter to predict diabetic nephropathy. There was a significant correlation among urinary TRF concentration, microalbumin, and N-acetyl-beta-D-glucosaminidase. The urinary excretion of TRF was more elevated than that of microalbumin. It is suggested that excretion of TRF in urine is a more sensitive index of the glomerular dysfunction in diabetes mellitus.