We determined plasma concentrations of cystatin C, beta2-microglobulin - beta2-MG (low molecular mass protein markers of glomerular filtration rate - GFR), creatinine (marker of GFR) and urinary N-acetyl-beta-D-glucosaminidase (NAG) excretion (marker of glomerular and tubular dysfunction) in 41 non-insulin-dependent diabetic patients. A significant increase of all the measured parameters (p<0.001, p<0.05, p<0.05 and p<0.001, respectively) in comparison to the control group, was observed. In the patients with microalbuminuria, only plasma cystatin C concentration and urinary NAG excretion increased significantly in comparison to patients with normoalbuminuria. At a cut-off level of 1.74 mg/l for cystatin C and 1.81 U/g creatinine for NAG (95% percentile of the normoalbuminuric group), the sensitivity of the tests for detecting microalbuminuria was 82% for cystatin C and 86% for NAG. The specificities were 88 and 92%, respectively. The present study demonstrated that determination of plasma cystatin C might be useful in the detection of incipient diabetic nephropathy and is a potentially better marker than creatinine or beta2-MG. No correlation between parameters measured in plasma or urine and glycated hemoglobin was found.