Thalidomide (Thal), a novel agent in the treatment of multiple myeloma, is presumed to act through a variety of mechanisms. In the present study, we examined the relationship between fibroblast growth factor receptor 3 (FGFR3) expression and the therapeutic effect of Thal. The DNA synthesis of KMS-11 clone, which overexpresses FGFR3, was inhibited by Thal in a dose-dependent manner; whereas U266 cells, which lack FGFR3 expression, failed to respond to Thal inhibition. To further examine the intertwining of Thal's therapeutic effects, wild-type human full-length FGFR3 cDNA was transfected into U266 cells. FGFR3 transfected U266 clones revealed increased FGFR3 expression, but resulted in decreased DNA synthesis and increased apoptosis under Thal treatment. Under Thal treatment, the myeloma proliferation-related protein, vascular endothelial growth factor (VEGF), and interleukin-6 (IL-6) were decreased in U266 FGFR3 transfectant as well. These results suggest that Thal inhibits myeloma cell proliferation and may depend on FGFR3 expression status. To further confirm this observation, we transfected a plasmid constructed anti-FGFR3 ribozyme (Rz52) into KMS-11 cells. In the ribozyme transfectant KMS-11 clone, FGFR3 expression was decreased; whereas the effects of Thal in cell growth inhibition were abrogated in KMS-11 Rz52 clone. Further results suggested that Thal inhibition of DNA synthesis, induction of apoptosis, and down-regulation of VEGF and IL-6 might be dependent on FGFR3-associated signal transduction of the ERK and STAT3 phosphorylation pathway. Thus, FGFR3 may be a predictive/surrogate marker for selection of Thal treatment in myeloma.