The concentrations of transforming growth factor- β(TGF- β) in platelets, plasma and urine from 27 patients with multiple myeloma (MM) and from 22 normal controls were measured by sandwich enzyme-linked immunosorbent assay using a monoclonal antibody specific for human TGF- β1+2+3. A significantly increased intraplatelet TGF- β(24.6 ± 9.6 vs. 17.8 ± 8.8 ng/l05 platelets, p < 0.01) and urinary TGF- β( 1.4 ± 0.8vs. 1.0 ± 0.4 ng/mg Cr, p < 0.02) were observed in MM patients compared with normal controls. The mean platelet TGF-β level in MM patients with osteolytic lesions was more increased than in those without osteolytic lesions (29.6 ± 7.7 vs. 18.4 ± 8.2 ng/l05 platelets, p < 0.001). In this study, we evaluated the possible role of TGF-β in the pathogenesis of myeloma, especially in osteolytic lesions.