Ovocystatin was isolated from hen egg white by affinity chromatog., thermally polymerized at 90 degrees C for 1.5 h, sepd. (dimer, tetramer, octamer) and studied for the inhibitory activity towards legumain. Dimer of ovocystatin retained 17% of its initial activity against legumain. The tetramer and octamer lost their ability to inhibit papain and legumain.