(1963) characterized four. All have similar but not identical amino acid composition, contain six or seven disulfide bonds and lack methionine and tryptophan. Molecular weights vary between 8,000-10,000. The complete amino acid sequence of component IV has been reported by Tan and Stevens (1971a and b). Krahn and Stevens (1972) report finding variations in activity of the four variants particularly with chymotrypsin, while essentially identical with respect to their trypsin inhibitory activity.