Cancer cachexia is one of the most common manifestations of advanced malignant disease and is frequently associated with decreased survival. Previously, we reported the establishment of a new anaplastic thyroid carcinoma cell line, Thena, and its mouse xenograft, Thena-Nu, which induced cachexia in athymic nude mice. Subsequent studies showed that the addition of clodronate to Thena-Nu cultures reduced cell proliferation as well as cytokine production in a dose- and time-dependent manner. Weekly administration of clodronate induced tumor cytostasis, attenuation of cachexia, as well as prolongation of survival in Thena-Nu-bearing mice. Reduced serum interleukin 6, tumor necrosis factor-alpha, and granulocyte colony stimulating factor levels were detected, whereas, serum leukemia inhibitory factor levels were not reduced. Liver necrosis, observed in tumor-bearing mice, was also improved following clodronate treatment. Discontinuation of clodronate treatment, however, resulted in progressive tumor growth and weight loss. Our results demonstrated that clodronate could exert therapeutic efficacy on amelioration of cancer cachexia in the hosts. Nevertheless, this study also points out that a longer period of treatment is required to maintain these effects.