The glycerol is quantitatively oxidized to formaldehyde by periodic acid, using a five minute oxidation period to minimize oxidation of glucose. The iodate and periodate are reduced to iodide by a large excess of sodium arsenite and the formaldehyde then determined directly in the oxidation mixture, by the color reaction with chromotropic acid. The precision of the method is about ± 2% in the range 2 to 8 p.p.m. of glycerol. The error due to glucose, in quantity equal to the glycerol, is only 2.5 to 5.0% and can be easily corrected for when the glucose content of the solution is known. One worker can analyze 40 to 60 samples per day.