We examined a number of seeds of gymnosperm and angiosperm species and found a large variation in trypsin inhibitor content (from 0 to ca. 100.000 units · g−1). The papain inhibitor content of the same seeds showed a smaller variation (1.7–31.7 units · g−1). During development of one of the seeds examined (cowpea, Vigna unguiculata) we observed that the papain inhibitor concentrations varied showing two maxima of activity linked to the phase of early seed growth and the seed filling stage, respectively. These different concentrations and ways of deposition of papain inhibitors as compared with trypsin inhibitors [20] suggest that they are associated with physiological/metabolic processes while the last ones are associated with defense mechanisms.