The inhibitory effects of gallium ethylenediamine-N,N,N',N'-tetrakismethylene phosphonate [Ga(III)-EDTMP] was studied on a malignant tumor and metastatic bone lesion model induced with Walker carcinosarcoma 256 (WCS 256) in Wistar rats weighing 120 to 135 g. A water-soluble chelate, Ga(III)-EDTMP, was prepared for injection in a tumor-bearing model. Radiographic analysis at 14 days indicated that the bone invasion and osteolysis were markedly reduced in animals treated with Ga(III)-EDTMP. The calculated tumor inhibitory rates were 33.16+/-0.38% at a dosage of 5 mg/kg and 47.75+/-0.74% at 10 mg/kg. Biochemical markers such as serum calcium decreased by 23% (P<.05) and by 31% (P<.01) at dosages of 5 mg/kg and 10 mg/kg, respectively, whereas serum alkaline phosphatase (ALPase) activity decreased by 47% (P<.01) and 69% (P<.01) at the 2 dosages.