In searching for a rapid and sensitive test to detect micro-inflammation in patients on hemodialysis (HD), we measured serum procalcitonin (PCT) levels and made a comparison with other traditional markers such as C-reactive protein (CRP), serum amyloid (SAA) and homocysteine, considered related to vascular damage. We investigated 51 HD patients, without signs of infection, in basal conditions (during standard bicarbonate dialysis and unselected filters: X) and after 4 months of possibly more biocompatible treatments (on-line hemofiltration (HF) or HD with ultra-pure dialysate and biocompatible membranes: Y). Serum PCT (measured by immunoluminometric assay), CRP and SAA (nephelometric assay) and plasma homocysteine (measured by high performance liquid chromatography) concentrations were assessed at the beginning of dialysis (T0) and after 4 hr (T4). Patients on unselected dialysis displayed mean PCT values significantly increased after 4 hr of dialysis in comparison to those at the start of the sessions (XT4 1.56 +/- 3.93 vs. XT0 0.4 +/- 0.34 ng/mL; p < 0.05). The PCT levels detected after 4 hr of biocompatible treatments were significantly lower than those detected after 4 hr of unselected treatments (YT4 0.78 +/- 0.34 ng/mL; p < 0.05), even though the percentage of patients with positive PCT values (> 0.5 ng/mL) remained almost unchanged. No significant modification in mean levels or in the frequency of positive values was observed for CRP, SAA and homocysteine. After 4 months of highly biocompatible treatments, a reduction in intradialytic enhancements of all inflammation markers was detected. Our data support the conclusion that PCT is a more precise marker than other traditional tests to evaluate micro-inflammation and biocompatibility in HD.