Ten HES cases, which satisfied the Chuside criteria are reviewed. We found several types of HES--mild forms, often accompanied by edema, and more severe forms accompanied by vascular, lung and heart disorders. It is not necessary to treat some milder forms while the more severe forms often respond to large dose of prednisolone. Now that the diseases, which share a common hypereosinophilic factor, have been defined and HES is being seen in variants of various diseases, the concept of HES has reached a turning point. The administration of appropriate treatment to the particular individual case appears to be advisable.