AbstractThe action of trypsin on the reserve proteins of the leguminous seeds belonging toVicieaeandPhaseoleaetribes was investigated. The hydrolysis of 11S and 7S proteins ofVicieaeproceeds relatively fast and some of the proteins are hydrolyzed practically completely. The hydrolysis of most of the investigated reserve proteins of thePhaseoleaetribe proceeds much slower, while that of 7S proteins of four Phaseolus species of American origin stops after the cleavage of only 10–20% of peptide bonds capable of reacting. Analogous results were obtained studying the action of chymotrypsin on a more restricted number of proteins. Both trypsin and chymotrypsin hydrolyze the same parts ofPh. vulgaris7S protein, splitting off peptides which can be separated on a Sephadex G‐50 column. The nonhydrolyzable high molecular weight core has a slightly smaller sedimentation coefficient and a higher electrophoretic mobility than the native protein and is able to dimerize at high ionic strength. Urea does not alter the hydrolyzability of the core butt the latter is partially hydrolyzed after the action of urea or guanidine hydro‐chloride in the presence of mercaptoet