Morphological changes of blood basophils activated by antigen and anti-IgE were discussed in relation to release mechanisms of the cells. 1. Basophils activated by antigen and anti-IgE show two different types : A form (pear-shaped) and B from (swollen type), on smear preparartions. 2. Pear-shaped basophils(reactive basophils), which appear after stimulation by antigen and anti-IgE, can be observed by the staining solution for the direct count of basophils and eosinophils. 3. The incidence of reactive basophils increases after addition of antigen. Thus, observation of reactive basophils can be clinically applied for detecting allergen (DCRB ; direct connt of reactive basophils). 4. Observation of morphological basophil response by phase- contrast microscopic motion pictures demonstrates that basophils activated by antigen show two different reponses, increase in motility (oriented movement) and degranulation.