Seed trypsin inhibitors have been purified from Pisum. Three groups of inhibitor were separated using column chromatography, whereas non-denaturing activity gels showed that five inhibitors could be distinguished. N-terminal sequence data obtained for two purified inhibitors showed that these belong to the Bowman-Birk class of inhibitors. Partial purification and characterization of a protease with in vitro trypsin-like activity from Pisum seed protein preparations indicated that this endogenous protease is not inhibited by any of the fractionated inhibitors