ASSAY techniques differ not only in the . calcium and phosphorus content of the assay diet, but also in feedstuffs used in the assay diet and the actual procedures. Ammerman et al. (1960) suggested a fourday depletion period followed by a six-day phosphorus supplementation period for a rapid assay of inorganic phosphates with chicks. Motzok et al. (1967) fed chicks four weeks when studying utilization of calcium and phosphorus from soft phosphate. Damron and Harms (1969) fed chicks the same diet from one to 21 days of age in developing a standard curve for Curacao Island phosphate Equally as confusing is the variety of feedstuffs used in the assay basal diet. Corn is generally used as the primary energy source, but some workers have used ground yellow corn (Motzok et al., 1967; Nelson and Peeler, 1961) while others have used degerminated corn meal (Ammerman et al., 1960; Dilworth and Day, . . .