A 45-year-old Japanese electrical engineer was admitted to our department of internal medicine on August 12, 2003, because of a sudden high fever and severe hypoxic respiratory failure. At a barbecue with his family on August 3 beside a nearby river, he had been exposed to the smoke. From August 4 to 11, he had suffered fatigue, fever, dry cough and progressive dyspnea. On admission, his SpO2 was 84%, and computed tomography scanning showed patchy ground glass opacity, thickened bronchial walls, and bilateral pleural effusions. The eosinophil count in the bronchoalveolar lavage fluid (BALF) was increased to 52.4%. Noticeably, the KL-6, SP-A and SP-D levels in the serum were elevated to 197 U/ml, 188 ng/ml and 137 ng/ml, and their levels in BALF had also increased to 225 U/ml, 890 ng/ml and 1110 ng/ml, respectively. The lymphocyte stimulation test was negative, and the cultures of blood and BALF did not grow any pathogens. The patient had smoked 1 pack of per cigarettes day for 25 years and showed no sign of atopic illness. Acute eosinophilic pneumonia (AEP) was diagnosed, and responded dramatically to treatment with oxygen and corticosteroids. The dissociation between the normal KL-6 levels and the elevated SP-A and SP-D levels in the serum and BAL fluid may play an important role in cases of AEP.