In a search for new biologic serum tumor markers with prognostic value we evaluated the soluble form of the CD30 (sCD30), a marker of cells producing T helper 2 (Th2)-type cytokines, interleukin-1 receptor antagonist (IL-1ra), soluble interleukin-2 receptor (sIL-2R), soluble tumor necrosis factor -type I, -type II (sTNF-R55, -75) and immunosuppressive acidic protein (IAP) in patients, with advanced colorectal cancer. The data showed that abnormal levels of sCD30 were detected in eight (80.0%) out of ten patients. In contrast, sCD30 levels were not detected in healthy volunteers. The relationship between sCD30, sIL-2R and IAP were positively correlated. In contrast, sCD30 and IL-1ra were negatively correlated. These results suggested that IL-1ra may play a role, at least in part, to inhibit CD30 release, and sCD30 appears to be a new biologic serum tumor marker of possible use in the clinical setting of cancer patients.