The action of pepsin on the 11-S and 7-S proteins of vetch, 11-S protein of soybean and 7-S protein of Phaseolus vulgaris was investigated. The first three proteins are hydrolyzed almost completely, the rate of hydrolysis being close to that of hemoglobin, while the hydrolysis of Ph. vulgaris 7-S protein stops after the cleavage of only 2,4% of peptide bonds. The nonhydrolyzable high molecular weight core makes up to 87% of the initial protein and differs from the latter in its electrophoretic mobility and sedimentation coefficient. The action of pepsin does not increase the digestibility of Ph. vulgaris 7-S protein by trypsin. After the consecutive action of these enzymes about two thirds of the protein remain unhydrolyzed. The digestion of Ph. vulgaris 7-S protein by pepsin is completed only after its denaturation by heat treatment or by the action of 6 M guanidine hydrochloride.