Cysteine proteases are proteolytic enzymes involved in many pathological processes. The role of cysteine proteases is crucial in normal cellular metabolism, being fundamental to intracellular protein turnover, collagen degradation, and cleaving of precursor proteins. Cysteine protease inhibitors, of which the cystatin superfamily are an example, constitute the final regulatory step in the control of cysteine proteases. In this study our first experience and comparison between a group of healthy volunteers and patients with sev eral renal disorders from the Dept. of Resuscitation and from the Haemodialysis Center are presented. Measurement of cystatin C in healthy volunteers demonstrates an agreement of our „physiological“ and „pathological“ values to references. Comparison of both classical calculated GFR values using levels of creatinine in plasma/urine and cystatin C levels in patients with renal dysfunctions from reanimation unit demonstrates applicability; investigation of cystatin, however, has not been influenced with errors based on collecting of urine. Currently, cystatin C is the most frequently investigated family member and is involved in processes such as tumour invasion and metasta- ses, inflammatory processes and some neurological diseases. In such diseases the emphasis is on a subtle balance and regulation of both the cysteine proteases and their inhibitors, with an imbalance resulting in a pathological state. In addition, the constant serum concentration of cystatin C means that it can replace creatinine in the measurement of the glomerular filtration rate. To date, several assays have been developed and studies show a promising future for its use in the medical laboratory, and not just as a research tool.

        Key words: cystatin C, glomerular filtration rate (GFR), creatinine clearance.