The seeds of plants often contain large amounts of proteins, which are subjected to extensive proteolytic processing during seed development and subsequent germination. One class of legume seed proteins, the Bowman-Birk-type trypsin inhibitors, has proved especially useful as a subject in studying these events. Sequence studies of the trypsin inhibitors from a number of legume species suggest that many of the inhibitors undergo a limited shortening at the amino terminus during seed development. However, during germination, the inhibitors appear to function as storage proteins. As such, they are subjected to extensive proteolysis, ultimately leading to their destruction. This degradative process has been studied extensively in the mung bean (Vigna radiata [L.] Wilczek). Proteolysis of the mung bean trypsin inhibitor involves, at least initially, an ordered sequence of limited proteolytic cleavages. The two proteases involved in the initial phases of this degradation have been identified and partially characterized.