Three murine sarcoma cells (Dunn osteosarcoma, Gunma clone-4, Sarcoma 1509a) were cultured for four days at various concentrations of CdCl2 or ZnCl2 and assayed for their viability. Dunn osteosarcoma was more sensitive to CdCl2 and less sensitive to ZnCl2 than the others. CdCl2 and ZnCl2 were weekly administered to C3H/He mice intraperitoneally from three days after the inoculation of Dunn osteosarcoma. The size of the tumors was measured twice a week for five weeks. CdCl2 suppressed the growth of the tumor, whereas ZnCl2 did not. These results suggest that CdCl2 has antitumor activity, especially against osteosarcoma.