By amking 1-ascorbic acid and molecular oxygens act upon methemoglobin the author studied the decomposition processes spectrochemically and obtained the following results. 1. In preparing methemoglobin from oxyhemoglobin with sodium nitrite no spectrochemical effect of sodium nitrite can be recognized on methemoglobin. 2. Methemoglobin is reduced to oxyhemoglobin in the presence of 1-ascorbic acid and molecular oxygen and thereafter it shows a similar decomposition processes as observable in the case of oxyhemoglobin. 3. This reaction is affected by molecular oxygens namely, when the quantity of molecular oxygen is large, the speed of the reaction is greater but the production of 670 mμ substance is inhibited; whereas when the quantity of molecualr oxygen is small, the absorption index of 670 mμ and 630 mμ substances is greater. 4. The 670 mμ and 630 mμ substances that are intermediate substances of this reaction are reversible to one another depending upon the quantity of moecular oxygen present. 5. This reaction is affected by the ion concentration; namely, between pH 6.8 and pH 7.7 at pH 7.2 the 670 mμ and 630 mμ substances are produced in the greatest amounts. 6. This reaction is affected by 1-ascorbic acid; namely, with the increase in the amount of ascorbia acid the speed of reaction is accelerated. 7. This reaction is affected also by temperature; namely, with a rise in temperature the reaction is accelerated whereas with a fall in temperature the reaction is retarded. 8. At an eary stage of this reaction dipyrromethen serlies substances are produced by the decomposition of the 670 mμ and 630 mμ substances.