EOSINOPHILS, like neutrophils and basophils, are a type of granulocyte derived from bone marrow, distinguished by their morphologic features, constituents, products, and associations with specific diseases. The original denominating property of eosinophils was the cardinal affinity of their cytoplasmic granules for acid aniline dyes, such as eosin. Eosinophils contain several eosinophil-specific proteins in their cytoplasmic granules, yet to date no cell-surface proteins unique to eosinophils have been recognized. Thus, tinctorial properties remain the routine basis for identifying and enumerating these leukocytes in blood and tissues. Eosinophilia, characterized by both heightened production of eosinophils in bone marrow and the accumulation of . . .