Following a previous note on the latest development in the study of eosinophilic granulocytes, a nosographic classification scheme is proposed for the problematic group of haematic eosinophilias. The scheme is based on the division of hypereosinophilias into three basic groups: benign idiopathic hypereosinophilias, hypereosinophiliasis caused by systemic eosinophilic blood diseases and symptomatic hypereosinophilias. Two rare events, hereditary familial eosinophilia and bening, non-familial idiopathic eosinophilia may be added to the benign idiopathic hypereosinophilias group. The group of hypereosinophilias caused by systemic eosinophilic blood diseases is still controversial and difficult to interpret. Particular attention is paid to the so-called "idiopathic hypereosinophilic syndrome" (HES), an umbrella term under which there is a current tendency to group a heterogeneous series of disorders characterised by long-lasting hypereosinophilia where there is no known reason for the increased eosinophilic granulocyte rate. Clinical and physiopathological features are then described to decide whether a given condition lies within the scope of this still little known syndrome.