A method of phosphorus determination adaptable to the phosphorylase enzyme system of waxy maize was developed after a critical study of the methods reported in the literature. This problem involved the construction of a photo-electric colorimeter, the selection of a suitable filter combination, the calibration of the instrument, and the standardization of the method of phosphorus determination;Preliminary studies were made to obtain an estimate of the role of phosphorylase in the development of the waxy maize, to show the trend of the equilibrium reaction of starch + inorganic-P &rlhar2; glucose-1-phosphate in the presence of phosphorylase, and to form a basis for further experiments in purification and concentration of the enzyme;Phosphorylase studies involved the necessity of the preparation of glucose-1-phosphate (the Cori-ester) in quantities suitable for use as substrate for enzyme action. The chemical, synthetic (rather than the enzymic) method of preparation of glucose-1-phosphate was used, and several adaptations of the previously reported methods are described;The Green and Stumpf method of expressing the activity of the enzyme in terms of phosphorylase units was studied and adapted to this work;Waxy maize collected from the field during the entire time of growth from 16 days after pollination to maturity was tested by precipitation of the enzyme from extracts and determination of the phosphorylase units present. Data for the 1942 corn showed a considerable activity of phosphorylase in the earliest corn tested (16 days after pollination). Phosphorylase precipitates were obtained from corn at the later stages of growth; these precipitates apparently exhibited fairly constant (or possibly decreasing) activity up to maturity. (Abstract shortened by UMI.)