We investigated the effect of oxidative systems on plasma proteins using Chloramine-T, a source of free radicals. Plasma specimens from 10 healthy volunteers were treated with 40 mmol/L Chloramine-T (1:1 v/v). Total protein and plasma carbonyl levels were evaluated spectrophotometrically. Identification of plasma proteins modifications was performed by SDS-PAGE, protein and lipid electrophoresis. Protein fragmentation was evaluated by HPLC. Total protein levels of oxidised plasmas were significantly lower (4.08 +/- 0.12 g/dL) than control (7.86 +/- 0.03 g/dL) (P<0.01). Plasma carbonyl levels were higher (1.94 +/- 0.38 nmol/mg protein) in oxidised plasma than that of control (0.03 +/- 0.01 nmol/mg protein) (P<0.01). Plasma oxidation had no significant effect on the levels of proteins and lipids. Protein fragmentations were detected in oxidised groups compared to those of the control. We conclude that protein modifications have direct effect on the protein functions, which are related to stress agent, its treatment period(s), and the methodology used for evaluating such experimental results.