A 57-year-old male patient with multiple myeloma showed an aggressive course with characteristic clinical features: rapid progression of plasmacytoma in the thoratic cavity, high serum levels of lactate dehydrogenase (LDH), which is usually not elevated in myeloma patients, and neutrophil infiltration in pleural effusion. Despite treatment with vincristine, doxorubicin and dexamethasone, the tumor mass had become non-responsive to chemotherapy and been increasing in size in correlating with the increase of serum levels of LDH. The patient died of respiratory failure 4 months after treatment. Thus the serum level of LDH is thought to be a useful clinical marker to monitor disease activity as well as other markers such as monoclonal immunoglobulin and beta 2-microglobulin. To investigate the cause of neutrophil infiltration into pleural effusion, we cultured plasma cells obtained from the effusion for 3 days in serum-free medium and examined the activity of neutrophil chemotaxis in the culture supernatant. The results showed chemotactic activity in the supernatant as high as in positive controls stimulated with a chemotactic factor, formyl-methionyl leucyl phenyl-alanine, suggesting that tumor cells produced neutrophil chemotactic factor(s).