A 45-year-old man was admitted to our hospital with chief complaint of fever. The chest X-ray examination showed 2-3 mm fine nodular shadows throughout the entire lung fields. Eosinophilia was present in the peripheral blood. Spike-like high fever (39 degrees C) appeared every 48 hours. All bacteriologic cultures from blood, bone marrow aspirate, sputum, gastric juice, and bronchoalveolar lavage fluid were negative. Furthermore, the antibody titer of malaria was negative. No antibiotics were effective in this case. Histological examination of the transbronchial lung biopsy showed non-specific inflammation, but the open lung biopsy specimen showed scattering of tiny granulomatous lesions. These granulomas were composed of histiocytes with indented nuclei, fibroblasts, varying amounts of collagen fibers, and eosinophils. The histiocytes were positive for S-100 protein staining and identified as Langerhans' cells. Therefore, this patient was diagnosed as having pulmonary eosinophilic granuloma. Two months later, the abnormal shadows on the chest X-ray and high fever spontaneously resolved without steroid therapy. This case was considered to be unique with respect to the peripheral blood eosinophilia, the three-day fever, and spontaneous improvement, compared with the former reported case.