Using a compound microscope and the blood of several animals (including the elephant!), the English anatomist, TW Jones, discovered, in 1846, that some white blood cells contained granules that became visible when immersed in hypotonic solutions (Jones, 1846). Although it has been claimed that Jones had discovered the eosinophil (Archer, 1963), it is more likely that he visualized the more abundant neutrophil (Spry, 1988). It was Brown (1898) who probably first detected eosinophils in the blood and bone marrow of patients with eosinophilic leukemia in the latter decades of the 19th century, although the lack of appropriate dyes and staining techniques at that time prevented formal identification. Full credit for the discovery of the “eosinophile” is thus given to Paul Ehrlich (1879) who first noticed that a certain population of white blood cells was stained with a negatively charged, brominated fluorescein compound, eosin, and was so named for that property. Despite the discovery of eosinophils almost 120 years ago, still relatively little is known of their biochemistry and pharmacology when compared to their highly studied sister cell, the neutrophil. This is perhaps surprising given the critical role of these cells both in host defense