Vesicular exudate was produced by the application of Unguentum Vesicans on the skin which was treated with various allergenic extracts. The exudate was than examined for the presence of basophils and eosinophils in 134 patients with bronchial asthma. The results were as follows. 1) Larger numbers of total white cells in the vesicle were seen at the sites of the skin test than at the untreated skin sites. 2) A slightly larger number of basophils and eosinophils was found in the vesicular fluid at the sites of skin, which demonstrated a positive immediate-type reaction, than in the sites of negative to an allergen. 3) Basophils appeared in relatively higher rate in the fluid of positive reaction to candida or ragweed than to house dust. A tendency of eosinophil migration into such vesicular lesions was about the same as basophil migration, although statistically not significant. 4) Basophils and eosinophils in the vesicular fluid with positive reaction using higher concentration of candida or house dust extract showed more increase than using lower concentration. It was found that both cells increased clearly around the concentration of house dust at the end point of the skin. 5) There was a relationship between basophil numbers in peripheral blood and those in the skin vesicles. In the cases with basophils in peripheral blood more than 65/cmm, basophil migration at the sites of skin lesions showed clear increase compared with the cases less than 65/cmm. Similar tendency was also found in eosinophils. A negative correlation between serum IgE level and intravesicular appearance rate of basophils was observed. 6) Among the patients with occupational asthma induced by inhalation of timber dust of Chinese quince or Rosewood and by inhalation of Buckwheat, basophils and eosinophils appeared in large numbers at the sites of a positive immediate skin reaction to the special allergen. 7) This study demonstrated that basophils as well as eosinophils can easily migrate from the blood vessels into extravascular tissues at sites of allergic reactions, especially in reaginic hypersensitivity. Both basophils and eosinophils or either cell alone appeared in large numbers at sites of positive immediate reactions if allergens were specific in individual cases. The skin vesicle technique discribed above may be of a great use for detecting allergens and evaluating allergic disease states.