Pleiotrophin (PTN), a tightly regulated angiogenic and mitogenic heparin-binding protein, is markedly elevated in a variety of aggressive solid tumours. The role of PTN in haematological malignancies, however, has not been previously evaluated. This study demonstrated that PTN serum levels were elevated in multiple myeloma (MM) patients when compared with healthy subjects (P < 0.0001). Serum levels of this protein significantly increased during progression of disease, and decreased during response to anti-MM therapy (P < 0.001). These results suggest that serum PTN may be a new biomarker for monitoring the disease status and therapeutic response of MM patients.