The aim of this study was to investigate the effect of desferrioxamine on peroxynitrite-mediated damage in erythrocytes by measuring the 3-nitrotyrosine level and glutathione peroxidase and Na+-K+ ATPase activities in vitro. 3-Nitrotyrosine levels were determined by HPLC; glutathione peroxidase and Na+-K+ ATPase activities were measured by spectrophotometry. Peroxynitrite increased the 3-nitrotyrosine level but decreased both enzyme activities. In the presence of desferrioxamine, glutathione peroxidase activity was increased with a decrease in the 3-nitrotyrosine level. Desferrioxamine was found to possess an important antioxidant activity as assessed in an in vitro system, reducing protein nitration, restorating enzyme activities and maintaining erythrocyte membrane integrity. Copyright © 2004 John Wiley & Sons, Ltd.