Eosinophilic lung disease is a heterogenous group of disorders that shares the feature of abnormally increased numbers of eosinophils within the pulmonary parenchyma. There have been no reports on pulmonary infiltration with eosinophils associated with syndrome of inappropriate secretion of antidiuretic hormone (ADH). A 67-year-old male was admitted to our hospital because of dyspnea, productive cough, and fever. On admission, leukocytosis (12,100/mm3) and eosinophilia (1,573/mm3) were found. Plasma IgE level (CAP) was more than 5,000 KU/L. However, specific antigen for eosinophilia was not detected by CAP and the skin prick test for common 55 inhalant allergens. Evaluation of parasitic infection including stool parasitic ova examination, serum parasite specfic IgG antibodies by enzyme linked immunosorbent assay (ELISA) was negative. High-resolution chest CT scans revealed extensive bilateral pulmonary infiltration. Examination of the Bronchoalveolar lavage fluid revealed eosinophilia (15%). Several abnormal laboratory findings were as follows; serum Na+ 113 mmol/L, serum K+ 4.3 mmol/L, serum osmolarity 269 mosm/ kg, urine osmolarity 356 mosm/kg, urine Na+ 95 mEq/L. Other laboratory examination showed that renal, adrenal, and thyroid function were normal. Serum ADH was not suppressed (1.5 pg/mL) in spite of hypoosmolarity of serum. Pulmonary eosinophilic infiltration was improved after treatment with prednisolone, but hyponatremia was persistent.