To investigate the influence of the thalidomide on the growth of multiple myeloma cells from untreated, relapsed or refractory patients and summarize its mechanisms, thalidomide influence on colony growth of untreated, relapsed or refractory multiple myeloma cells cultured by semisolid methylcellulose was observed. The level of interleukin-6 (IL-6) autosecreted by myeloma cells was tested by IL-6-dependent cell line when myeloma cells were treated with thalidomide at 200 microgram/ml, and in the same concentration of thalidomide the expression of IL-6 receptor were tested by flow cytometry. Results showed that colony growths of myeloma cell from untreated and relapsed or refractory patients were all colonies were inhibited when treated by thalidomide up to 75 microgram/ml or 100 microgram/ml concentration. The inhibition was concentration-dependent, higher concentration cause more inhibition. After treatment with thalidomide at 200 microgram/ml, the concentrations of IL-6 secreted by myeloma cells were (148.5 +/- 96.7) microgram/ml, and the levels of IL-6 receptor expressed on the cell surface were 16.7% and 20.2% in untreated and relapsed or refractory patients, respectively, and those were significantly lower than those levels in the cells before exposure to thalidomide. It was concluded that thalidomide can inhibit growth of both relapsed or refractory cells and untreated myeloma cells in vitro. Therefore, it can be used to treat untreated multiple myeloma patients. Inhibiting tumor cells secreting level of IL-6 and reducing the expression of IL-6 receptor on myeloma cell surface is one of the mechanisms for thalidomide to remedy multiple myeloma patients