The need for delivering to the market citrus fruits of the highest possible internal quality promoted interest in the possibility of the association of marketable quality with some measurable entity other than the commonly used ratio of total soluble solids to titratable acidity. In the course of investigations of the changes in nitrogenous constituents during the maturation of orange fruits, it was possible to gather data which demonstrate the changes in the concentration of certain constituents of the juice which occur during the development and ripening of these fruits.