A method based on high performance capillary electrophoresis (HPCE) has been developed for identification and quantitative determination of inhibitors from leguminous seeds. The method allows specific characterization of Kunitz soybean trypsin inhibitor (KSTI) and Bowman Birk inhibitor (BBI) from soybean (Glycine max., L.). Standard curves for the inhibitors showed a satisfactory linearity between normalized peak area and sample concentration, and a good repeatability of the method was found. Identification of protein peaks as proteinase inhibitors was based on their binding to trypsin. The system also proved useful for determination of the number and specificity of inhibitor sites on the individual inhibitors and for binding studies with monoclonal antibodies against the inhibitors.