The oxidative modification of human hemoglobin (Hb) treated with hydrogen peroxide was investigated. Using the mass spectrometry method, the oxidized amino acid residues of the hemoglobin molecule were detected: αTrp14, αTyr24, αArg31, αMet32, αTyr42, αHis45, αHis72, αMet76, αPro77, αLys90, αCys104, αTyr140, βHis2, βTrp15, βTrp37, βMet55, βCys93, βCys112, βTyr130, βLys144, and βHis146. The antioxidant potential of the Hb molecule in the intracellular space and in the blood plasma is discussed.