Murine colon 26 adenocarcinoma causes a progressive weight loss and physiological changes associated with cachexia when it grows to a certain size. By the use of this tumor model several types of cytostatics were examined for their ability to alleviate cachexia. Among them, 5′-deoxy-5-fluorouridine could reverse a progressive weight loss and improve hypoglycemia, hyperglucocorticism, and hepatic malfunctions, as well as inhibiting the tumor growth. Cyclophosphamide, nimustine, and 2′-deoxy-5-fluorouridine were only slightly effective in reversing the wasting, while 5-fluorouridine, tegafur, mitomycin C, cis-platinum, and doxorubicin were not active. Within 3 days after 5′-deoxy-5-fluorouridine was administered to cachectic mice with large tumor burdens, the wasting was immediately reversed even at doses in which there was increase or no significant reduction in tumor growth. These results indicate that the anticachectic activity of 5′-deoxy-5-fluorouridine is independent of its antiproliferative activity.