Proteinuria is a risk factor for end-stage renal disease (ESRD). Creatinine clearance (CrCl) is usually used as a marker to monitor the progression of ESRD, while cystatin C (CYST) has also been considered as a marker of renal function. Tumor-associated trypsin inhibitor (TATI) has been shown to be a promising marker of renal function. The aim of this study was to examine the relationship between CrCl, CYST, ß(2)-microglobulin (B2M) and TATI, with glomerular filtration rate (GFR) in patients with different levels of proteinuria.