The aim of this stud), 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; gluthione 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 (C) 2004 John Wiley Sons, Ltd.