Recently, when determinations of inorganic phosphate in mixtures containing sodium glycerophosphate (used as a substrate in plasma phosphatase determinations) were required, the use of heat involved in the Benedict-Theis method rendered it obviously unsuitable. The many advantages of the Kuttner-Cohen method,1 with the modifications later suggested by Kuttner and Lichtenstein2 and Raymond and Levene,3 recommended themselves to us. We found this method capable of yielding very accurate results (within ±2% of the known quantities), after correction for the considerable deviations from the “Beer law”. These deviations were determined by a large number of analyses, charts were constructed and tables compiled for more convenient reading.We use 1 cc. of plasma when it is expected to contain 5 mg. of phosphorus per 100 cc. or more, and 2 cc. of plasma when it is expected to contain less. Ten cc. of water are added and 5 cc. of 10% trichloracetic acid. About 14 cc. of filtrate are available. Four cc. of the acid-...