The vicilin and phaseolin proteolysis by papain at acidic pH has been studied in vitro. It has been found that vetch vicilin is practically completely degradated at pH 4.6. The phaseolin hydrolysis differs from that of vicilin, phaseolin being only modifi ed by papain. This modifi cation results in the formation of fragments that correspond to half subunits of native phaseolin that are resistant to further action of papain. These fragments remain associated in molecule’s quaternary structure producing phaseolin-Pap. The phaseolin modifi ed at pH 4.6 becomes insoluble, while at pH 5.6 it is soluble. These fi ndings show that while the action of papain on vicilin is similar to the action of endogenouse papin-like proteinases its action on phaseolin is slightly different.