The appearance of basophils and eosinophils at the sites of late or delayed skin reaction was examined in 34 bronchial asthmatics. Using guinea pigs, basophils at the site of cutaneous basophil hypersensitivity were observed with electron microscopy. The results were as follows. 1) The numbers of basophils and eosinophils increased significantly at the sites of positive delayed skin reaction to PPD and various allergens. Furthermore, the above phenomenon was much more conspicuous and significant at the sites of positive late reactions than of negative ones. 2) The appearance of basophils showed two peaks, i.e., at 30 minutes and 6 hours, after intradermal allergen injection. Eosinophils appeared at 6 hours in the peak. 3) In the cutaneous basophil hypersensitivity, migrating basophils and eosinophils were observed around the blood vessels in the hypodermis of guinea pigs. Electron microscopic observations demonstrated that basophils showed exocytotic degranulations were sometimes phagocytized by macrophages.