The article focuses on one of rarely occuring forms of "major eosinophilias"--hypereosinophilic syndrome (HES). Based on two observations and data from the published literature the clinical presentation of HES is described together with affection of different organs, changes in the blood and bone marrow. The article has a particular focus on differential diagnosis of HES, symptomatic and clonal eosinophilias, importance of cytogenetic investigations. The policy of managing patients presenting with the above medical problem is discussed.