Eosinophilic granulocytes are the main defense cells against parasitic infection. Why these cells also play a major role in allergic diseases and in drug reactions is not solved. However, there is some knowledge, which might explain their role in such diverse inflammatory reactions. The eosinophil can react pro-inflammatory as well as anti-inflammatory. The cells contain toxic proteins such as major basic (cationic) protein, exotoxin, and neurotoxin, which are stored in their large secondary granules, but also contain anti-inflammatory proteins, such as a leucin-aminodipeptidase and histaminase stored in the small granules. We briefly will discuss allergic mycosis; however, the main focus will be on eosinophilic pneumonia and their many different causes.