P u r p o s e: Methemoglobinemia is a disorder caused by over accumulation of methemoglobin in the red blood cells of circulating blood, prohibiting adequate supply of oxygen to organs. The seriousness of its clinical symptoms and its treatment methods are determined by the blood methemoglobin level. Therefore, we revealed the clinical relation between the blood methemoglobin level and oxygen saturation on a pulse oximeter. Then we tried to indirectly measure the blood methemoglobin level by using their relation, instead of checking its level through blood sampling. M e t h o d s: The medical records of 39 patients who were admitted to the Chonnam University Hospital Emergency Medical Center due to acute methemoglobinemia between January 1, 2001, and June 30, 2005, underwent a prospective analysis.