SUMMARYNitrogenous constituents of developing pineapple fruit were determined at weekly intervals on two lots of fruit in 1958 and four lots in 1963. Some analyses on shell tissue were included. The fraction of nitrogen in the flesh of the fruit not precipitated by trichloroacetic acid or by heating fell during the prematuration period, then rose during the final weeks of development. By contrast, the concentration of heat‐soluble nitrogen in the shell fell throughout fruit development. Many of the constituent free amino acids in the juice also showed a minimum concentration during the middle of the developmental period, or maturation. The notable exception to the nitrogen trends was methionine, which was generally absent until onset of final ripening but present in considerable amounts thereafter. Protein concentration rose during the first weeks after cessation of flowering, then dropped somewhat during the remainder of fruit development. Little or no protease activity was found in the flesh of fruit shortly after flowering, but the enzyme then appeared abruptly and remained at a high level during fruit development, dropping only during the final period of ripening. Peroxidase activity was high in the young fruit and fell steadily throughout fruit development, reaching a minimum during ripening. At this time, the activity was only a third that of the fruit shortly after flowering. The trends in nitrogenous constituents reinforced the earlier suggestion of several discrete physiological stages in the development of the pineapple frui