We investigated the effects of pulsed magnetic stimulation on tumor development processes and immune functions in mice. A circular coil (inner diameter 15 mm, outer diameter 75 mm) was used in the experiments. Stimulus conditions were pulsewidth 238 ms, peakmagnetic field 0.25 T (at the center of the coil), frequency 25 pulses/s, 1000 pulses/sample/day and magnetically induced eddy currents in mice 0.79–1.54 A/m2. In an animal study, B16-BL6 melanoma model mice were exposed to the pulsed magnetic stimulation for 16 days from the day of injection of cancer cells. A tumor growth study revealed a significant tumor weight decrease in the stimulated group (54% of the sham group). In a cellular study, B16-BL6 cells were also exposed to the magnetic field (1000 pulses/sample, and eddy currents at the bottom of the dish 2.36–2.90 A/m2); however, the magnetically induced eddy currents had no effect on cell viabilities. Cytokine production in mouse spleens wasmeasured to analyze the immunomodulatory effect after the pulsedmagnetic stimulation. tumor necrosis factor (TNF-a) production in mouse spleens was significantly activated after the exposure of the stimulus condition described above. These results showed the first evidence of the anti-tumor effect and immunomodulatory effects brought about by the application of repetitive magnetic stimulation and also suggested the possible relationship between anti-tumor effects and the increase of TNF-a levels caused by pulsed magnetic stimulation. Bioelectromagnetics 27:64–72, 2006. 2005 Wiley-Liss, Inc. Key words: tumor weight; cytokine production; TNF-a production; B16-BL6 melanoma