A 75-year-old man with multiple myeloma presented with fever and respiratory symptoms. A chest roentgenogram showed interstitial shadows and transbronchial lung biopsy revealed diffuse infiltration of amyloid in the alveolar walls. Analysis of bronchoalveolar lavage fluid showed the presence of an IgA-lambda paraprotein, and the IgA/albumin ratio was similar to that in serum. However, plasma cells could not be detected in the cells obtained by lavage. We know of no previous case in Japan in which bronchoalveolar lavage fluid was examined in a case of diffuse alveolar septal amyloidosis.