Transient peripheral eosinophilia occurs in several disorders, such as allergic diseases, cancer, and parasitic in fections. However, in most cases, their persence is not accompanied by tissue destruction or organ dysfunc tion. In certain disease states, eosinophils can accumulate in any organ in the body and cause tissue destruction as a result of the eosinophil infiltration or the toxic effects of the degranulated proinflammatory products. Idiopathic hypereosinopilic syndrome is a rare disorder characterized by persistent eosinophilia of an unknown origin, usually associated with a dysfunction of organs such as the heart, lung, skin, and nervous system. Idiopathic hypereosinophilic syndrome usually has an indolent course over a period of several months. However, in some cases, they have grave symptoms if vital organs such as heart and lung are infiltrated.