Summary.A new method for the determination of carbon monoxide in blood is described. The blood is brought into an Erlenmeyer flask, mixed with water and its carbon monoxide hemoglobin is converted into acid hematin by addition of sulfuric acid. The carbon monoxide liberated passes into another Erlenmeyer flask, which has been connected with the first one by an airtight rubber cuff and contains a known solution of palladium chloride. A corresponding quantity of the latter is reduced to metallic palladium. Excessive palladium chloride is precipitated by a known quantity of potassium iodide, and the excess of the latter is titrated after the principle of Dupré‐Winkler. The method is well fitted for micro‐anal