A patient had systemic amyloidosis that extensively involved the lungs and breasts. Diffuse parenchymal pulmonary amyloidosis is rare but well described. Involvement of the breast in systemic amyloidosis is, however, most unusual. This patient's amyloidosis was associated with diffuse plasmacytosis and a kappa-chain gammopathy. The plasmacytosis was most prominent in the renal interstitium. Immunoperoxidase staining of the renal infiltrate and breast demonstrated IgG/kappa-staining plasma cells exclusively, suggesting that these cells were a monoclonal proliferation that contributed to the patient's M-protein and possibly to the patient's amyloid deposits.