AN AGGRESSIVE, terminal phase of plasma cell myeloma has been recently recognized.1,2 It is usually characterized by fever, pancytopenia, rapidly enlarging soft-tissue masses, and decreasing or stable levels of myeloma protein, with tumor morphological characteristics similar to those of a poorly differentiated or large-cell lymphoma. Death usually ensues in two to six months. We describe herein a patient with multiple myeloma whose condition had remained in plateau phase3 for five years and who then had an acute pneumonialike illness with rapidly progressive pulmonary infiltrates and fever, leading to his death due to respiratory failure within several days. Both antemortem and postmortem tissue examination conclusively showed that the pulmonary infiltrates were due to plasma cell invasion and not infection. Results of serial measurements of serum protein spikes as well as bone marrow studies, including thymidine-labeling indices4 and in vitro stem-cell drug sensitivity assays,5 throughout the course of