The run of trained rats until exhaustion affected changes of red-ox balance in red blood cells (RBC) and deteriorated the acid stability of RBC. The oral administration of quercetin, 20 mg/kg, caused expansion of oxidative stress in RBC and a significant decrease in RBC acid stability. Pro-oxidant activity of quercetin could contribute accelerated intravascular hemolysis. It was accompanied by a significant reticulocytosis compared with a control group of rats no fed on antioxidant but exposed to run. Green tea extract (GTE) oral administration, 12 mg/kg, resulted in preventing oxidative stress in RBC, increasing in acid stability of RBC and reducing reticulocytosis. Thus, prooxidant activity of quercetin and the high antioxidant efficacy of GTE are indicative of the advantages of the complex preparations containing several antioxidant compounds. Such complex preparations may counteract an oxidative stress and save mechanical stability of erythrocytes under exhausted run.