The eosinophil granulocyte is a pro-inflammatory cell which in its granules contains an abundance of highly cytotoxic proteins such as eosinophil cationic protein, eosinophil-derived neurotoxin, eosinophil peroxidase, eosinophil protein X and major basic protein. Upon stimulation of the cell, these proteins as well as a number of lipid mediators such as leukotriene C4, prostaglandin and platelet-activating factor are released to the exterior. The molecules which are produced during inflammatory reactions of the allergic type attract eosinophils to the target organ and stimulate them to liberate their products. The physiological meaning of this reaction is probably to combat invading parasites; however, in their absence accumulation and activation of eosinophils may cause disease, and one such disease may be chronic asthma.