Four isoinhibitors against bovine pancreatic trypsin were purified from Phaseolus vulgaris(cv. Tora-mame) seeds by extraction with water(pH 2.0), ammonium sulfate fractionation, gel chromatography on Sephacryl S-200, trypsin-Sepharose gel affinity chromatography, and chromatofocusing. They inhibit both trypsin and chymotrypsin strongly. Their molecular masses are 85 kDa, estimated by sodium dodecyl sulfate polyacrylamide gel electrophoresis. Their isoelectric points range 5.09 to 4.46. They are high in the content of aspartic acid, serine, proline, and half-cystine but low in valine, methionine, tyrosine, and phenylalanine. Tryptophan is absent from them completely. They are bound to both trypsin and chymotrypsin with equimolar ratio, and have separate and independent binding sites for both proteases. Chemical modification showed that the inhibitors are of lysine type.