Idiopathic pulmonary alveolar proteinosis (PAP) is a rare lung disorder characterized by excessive accumulation of surfactant lipoprotein in alveoli, which is caused by autoantibody against granulocyte-macrophage colony-stimulating factor. The case of a 42-year-old man with idiopathic PAP, who had worked in steel and cement plants for the past 10 years, is presented. His serum anti-GM-CSF antibody level was markedly increased. Lung specimens obtained during video-assisted thoracoscopic surgery were examined on immunohistochemistry using mAb for localization of surfactant proteins A and D (SP-A and SP-D) and a mucin-like protein, KL-6. Furthermore, western blot analysis of his bronchoalveolar lavage fluid (BALF) was performed using anti-SP-A and anti-SP-D mAb. As well as KL-6, SP-A was localized in the intra-alveolar fine granular substances. But on HE staining the SP-D was localized in SP-A-negative foci corresponding to eosinophilic large globules that were surrounded by an SP-A-positive fine granular structure. On western blot the specificity of mAb was shown. In conclusion, this is the first report demonstrating the striking difference in the distribution of SP-A and SP-D in the intra-alveolar substance of a patient with idiopathic PAP.