The intraperitoneal implantation of the ascitic hepatoma cells, AH-130 to rats induced marked atrophy of the systemic organs within 2 weeks, resulting in the animal death. By the method of Feulgen hydrolysis curve analysis, the amount of single-stranded DNA and the degree of DNA instability were shown to be increased in these atrophic organs. In keeping pace with the progression of the cachectic multi-organ damage (MOD), the amount of lipidperoxide and the activity of superoxide dismutase (SOD) as measured by electron spin resonance (ESR) were increased in the ascites toward the end stage of chachexia. The increased lipidperoxide and SOD induction reflect the increased production of active oxygens, especially superoxide. The marked systemic organ damage induced in cancer cachexia seems to be due to DNA damage by active oxygens.