Serum concentration of soluble interleukin-2 receptor (sIL-2R) was measured in noncachectic patients with 42 gastric and 32 colorectal cancers, 39 cachectic cancer patients and 15 normal volunteers. It increased with the advance of cancer, being highest in the cachectic patients. It was inversely correlated with the serum concentrations of nutriotional parameters such as prealbumin and transferrin, and positively correlated with the serum concentration of immunosuppressive acidic protein, soluble tumor necrosis factor receptor 1 and neopterin. The length of survival of cachectic patients (days) was inversely correlated also with the serum concentration of sIL-2R. These findings suggest that sIL-2R might be of use an important parameter to predict the progress of gastric and colorectal cancers, deterioration of the patients' nutriotional status and immune activity as well as their prognosis.