To clarify the action of IgG antibody on basophils in intractable asthmatics, morphological changes, density and redistribution of IgG antibodies on basophils were observed by immunoscanning electron microscopy. Pear-shaped basophils appeared more frequently in severe asthmatics than in nonsevere asthmatics when anti-IgG was added. The density of IgG antibodies bound to basophils was significantly higher in severe, but steroid-independent, asthmatics than in non-severe asthmatics and in steroid-dependent asthmatics (p<0.001). Cap and patch formations of IgG receptors on the cell were more frequent in severe asthmatics than in non-severe asthmatics. These findings suggest that the reactivity of basophils mediated by IgG antibodies is enhanced according to the severity of asthma, indicating that IgG antibodies act as anaphylactic antibodies in severe asthmatics, although IgG antibodies bound to the cell decrease during long-term steroid therapy.