Naringin and naringenin protect hemoglobin from nitrite-induced oxidation to methemoglobin. The protection is not observed when naringin and naringenin are added after the autocatalytic stage of the oxidation of hemoglobin by nitrite. The ability of naringin and naringenin to scavenge oxygen free radicals may be responsible for the action because superoxide, hydroxyl and other free radicals are implicated in promoting the autocatalytic stage of oxidation of hemoglobin by nitrite. Both compounds showed less ability to protect intact erythrocytes suggesting that they may not cross the erythrocyte membrane in sufficient amounts. Naringenin was more effective than naringin, probably because of the extra phenolic group in the aglycone.