In this modification of the method of Fiske and Subbarow, up to 2 ml. of the sample and 0.5 ml. 10 N H 2 SO 4 were heated at 150 to 160 C. for at least 3 hr. Two drops of 30 per cent. H 2 O 2 were added and the solution was heated for another 1 1/2 hr. After addition of 4.6 ml. 0.22 per cent. ammonium molybdate and 0.2 ml. of the reagent (0.5 g. 1-amino-2-naphthol-4-sulphonic acid mixed with 200 ml. 15 per cent. NaHSO 3 and 1 g. Na 2 SO 3 and the solution filtered) the solution was heated for 7 min. in boiling water and the optical density was measured at 830 mµ. A procedure for inorganic phosphate is given also. When it was mixed with phosphate esters the original Fiske Subbarow method was most reliable but not ideal. A. Hepburn.