Cytokine production was investigated in whole blood cell cultures from 74 patients with colorectal carcinomas, 20 patients with benign colorectal tumors, and 314 healthy controls. In the 4 day post induction supernatants the levels of IFN-gamma, IL-1-alpha, IL-2, and TNF-alpha were measured by a sensitive immunoassay. In the blood cell cultures of the patients with colorectal carcinomas significantly lower values of IFN-gamma (P less than or equal to .001), IL-1-alpha (P less than or equal to .001), and IL-2 (P less than or equal to .01) were found as compared to the patients with benign tumors and the controls, although total and differential leukocyte counts were similar in all three groups. A linear correlation between the levels of IFN-gamma and IL-1-alpha and the tumor stages could be shown. Our results suggest that a growing tumor burden may induce increasing immunological deficiencies as reflected by a decreasing cytokine production of the immune cells.