Two spontaneous cases of canine disseminated hypereosinophilic disease were experienced. Main clinical signs were weight loss, severe dyspnea and coughing with abnormally high level of IgG, and in one case (Case A), bloody diarrhea occurred shortly before death. At necropsy, fibrous neoplastic nodules about 4 cm in diameter were produced around the trachea in both cases. Similar nodular lesions as well as some diffuse ones, were disseminated in the lungs, liver and spleen. In addition, the skin and gastrointestinal tract were severely affected in case A, while the kidneys and lymphoid tissues were involved in Case B. Histopathologically, all the lesions consisted of proliferated and sometimes degenerated fibrous tissues with dense accumulation of eosinophil leukocytes and plasma cells. By electron micro-scopy some eosinophils were shown to have specific granules of normal shape showing a degranulation process. The findings suggested an immunologic mechanism involved in pathogenesis of the disease.