An alpha-amylase inhibitor (called the 0.53-inhibitor, Maeda, K., Takamori, Y. and Oka, O. (1982) Agric. Biol. Chem. 41, 2873-2875) and the carboxymethylated inhibitor were used to immunize mice (strain BALB/c) according to a procedure described earlier (McMaster, W.R. and Williams, A.F., (1979) Eur. J. Immunol. 9, 426-433). After fusion of spleen cells with NS-1 myeloma cells, three stable clones producing antibodies against the inhibitor were obtained. The binding characteristics of the monoclonal antibodies, AWAI-1, AWAI-2 and AWAI-3, to the inhibitor were analyzed by radioimmunoassay. Two of these monoclonal antibodies to the alpha-amylase inhibitor did not show any binding affinity towards carboxymethylated inhibitor, suggesting that the main antigenic determinant on the native inhibitor is tertiary-structure dependent. The monoclonal antibodies obtained cross-reacted with three other alpha-amylase inhibitors (the 0.19-, the 0.36- and the 0.38-inhibitor) in wheat and these were separated together with the 0.53-inhibitor from the rest of inhibitors by immunoaffinity chromatography. One stable clone producing antibody against the carboxymethylated inhibitor was also established, AWAI-4. The antigenic determinant to this antibody was found to be included in the region of Met(5)-Lys(25) on the carboxymethylated inhibitor.