Cancer cachexia is a syndrome of progressive wasting which is believed to be mediated by tumor necrosis factor-alpha, interleukins 1 and 6, and interferon-gamma, and leukemia-inhibitory factor. However, the levels of these putative agents do not correlate with cachexia. Recently, a new circulating tumor factor, termed cachectic factor (CF), has been isolated and characterized from the urine of mice transplanted with adenocarcinoma MAC16 (1). Purified CF, a proteoglycan of relative mol. Wt of ~24kD, produces cachexia in vivo by inducing catabolism of skeletal muscle. CF was also found in urine of cachectic cancer patients. It is not found in normal urine, patient with weight loss due to trauma, and cancer patient with no weight loss (1). CF appears to be ~24kD on SDS-gels. It is a sulfated glycoprotein. The amino acid analyses was determined as: YSP EAA SAP GSG DPS HEA. An antibody raised to the CF also recognized a 69kD band with the same amino acid sequence as the 24kD material.