Wheat (Triticum aestivum L) seeds contain a proteinaceous α-amylase inhibitor. We estimated the amount of the inhibitor that can bind to α-amylase rather than the total amount of the inhibitor, using an ELISA method. During 48 h of imbibition, the amount of the inhibitor did not change, while α-amylase activity increased rapidly. These results suggest that α-amylase synthesized de novo does not bind to the inhibitor. To examine further the interaction between α-amylase and its inhibitor, we localized immunohistochemically both α-amylase and the inhibitor in germinating seeds. In the embryo, we observed α-amylase only in the scutellar epithelial cells at 24 h after the start of imbibition, and later in the scutellar parenchyma cells. The inhibitor, on the other hand, was present between the scutellar parenchyma cells of the embryo at 0 h and 24 h after the start of imbibition, and disappeared later. α-amylase is separated from the inhibitor in the embryo. In the endosperm, we detected α-amylase in the aleurone cells at 24 h after the start of imbibition and later in the starchy endosperm. The inhibitor was present in the aleurone cells and starchy endosperm of the dry seed. During imbibition, the inhibitor in the starchy endosperm disappeared from the area to which α-amylase was secreted. It appears that α-amylase in the starchy endosperm also does not interact with the inhibitor. The aleurone cells are the only place that α-amylase can come into contact with the inhibitor. But, early secretion of α-amylase from the aleurone cells after imbibition started, and rapid disappearance of the inhibitor in the aleurone cells suggest that the α-amylase inhibitor does not work as an effective inhibitor of the endogenous α-amylase synthesized following germination.