It was extremely difficult to phenotype basophils because they are most sparse among blood leukocytes. We developed a new method which identified basophils on the basis of negative reactivity with mixed monoclonal antibodies (CD2, CD14, CD16, CD19). Using this method we could detect Fc gamma R II (CDw32) but not Fc gamma R I (CD64) on basophil surface. The method seems useful for the study of clinical allergy and also of the biology of basophil.