Systemic and local cytokine environment may modulate the immunogenicity of colorectal cancer cells, and affect anti-tumor immune functions of tumor-infiltrating lymphocytes. We therefore investigated cytokine mRNA expression patterns in tumors and peripheral blood mononuclear cells (PBMC) from patients with colorectal adenocarcinoma. IL-2, IFN-gamma, tumor necrosis factor-alpha (TNF-alpha), IL-4, IL-6, IL-8, IL-10 and IL-1 beta mRNAs in single cell suspension of freshly isolated colorectal cancer tissue were studied by RT-PCR. Frequencies of cytokine gene expression were compared to those in normal colonic mucosa from tumor patients. The frequencies of IL-2, IFN-gamma, IL-4 and IL-10 gene expression were also determined in peripheral blood mononuclear cells from patients with colorectal adenocarcinoma and compared to those of healthy individuals. Tumor samples were more frequently positive for IFN-gamma, IL-2, TNF-alpha and IL-10 gene expression than normal mucosa (p=0.0001, p=0.0118, p=0.001 and p<0.0001, respectively). Frequencies of IL-2 and TNF-alpha gene expressions were significantly higher in tumors with a diameter <5 cm, than in those with a diameter >5 cm. The genes for IL-6, IL-1 beta and IL-8 were commonly expressed in both tumor tissue and normal colonic mucosa. IFN-gamma transcripts were detected in more PBMC samples from patients with colorectal cancer than those from normal controls (p=0.0449). Thus, colorectal cancer tissue is characterized by a specific pattern of cytokine gene expression. It is likely that multiple interactions between pro- and anti-inflammatory cytokines regulate tumor growth and the functional activity of tumor-infiltrating lymphocytes.