Preliminary determination of the nutritional constituents of 19 wild leguminous seeds suggested their possible inclusion in animal nutrition. Since the whole seeds proved unpalatable as well as toxic, it was thought that their proteins might be extracted and used instead. Accordingly, simple and effective methods were standardized for isolation of proteins by subjecting defatted Phaseolus seeds to extraction studies. Distribution of total nitrogen and dispersion of nitrogenous constituents in the seeds were also studied. Proteins of considerable purity are best extracted with sodium chloride solution (5%, w./v.), with subsequent dialysis of the extract. Proteins were isolated from four varieties of Phaseolus seeds and their protein efficiency ratio and biological value evaluated by animal experiments with and without supplementing diets with the missing essential amino acids. © 1969, American Chemical Society. All rights reserved.