It has been established that overproduction of reactive oxygen species (ROS) occurs during hemodialysis causing oxidation of proteins. Alpha-1-antitrypsin is the major circulating anti-protease which contains methionine in the active site. The aim of the present study was to measure the level of serum trypsin inhibitory capacity (sTIC) in hemodialysis patients. This case-control study was performed in 52 hemodialysis patients and 49 healthy controls. sTIC was measured by enzymatic assay. The sTIC was significantly (P< 0.001) lower in hemodialysis patients (1.87 +/- 0.67 micromol/min/mL) than healthy controls (2.83 +/- 0.44 micromol/min/L). Reduction of sTIC may be due to the oxidation of methionine residue in the reactive site of alpha-1 antitrypsin.