AIM: To study the influence of tumor removal on the serum level of IgG antibodies to tumor-associated Thomsen-Friedenreich (TF), Tn carbohydrate epitopes and xenogeneic αGal, and to elucidate on the change of the level during the follow-up as well as its association with the stage and morphology of the tumor and the values of blood parameters in gastrointestinal cancer. METHODS: Sixty patients with gastric cancer and 34 patients with colorectal cancer in stages Ⅰ-Ⅳ without distant metastases were subjected to follow- up. The level of antibodies in serum was determined by the enzyme-linked immunosorbent assay (ELISA) using synthetic polyacrylamide (PAA) glycoconjugates. Biochemical and haematological analyses were performed using automated equipment. RESULTS: In gastrointestinal cancer, the TF antibody level was found to have elevated significantly after the removal of G3 tumors as compared with the preoperative level (U = 278.5, P < 0.05). After surgery, the TF and Tn antibody level was elevated in the majority of gastric cancer patients (sign test, 20 vs 8, P < 0.05, and 21 vs 8, P < 0.05, respectively). In gastrointestinal cancer, the elevated postoperative level of TF, Tn and aGal antibodies was noted in most patients with G3 tumors (sign test, 22 vs 5, P < 0.01; 19 vs 6, P < 0.05; 24 vs 8, P < 0.01, respectively), but the elevation was not significant in patients with G1 + G2 resected tumors. The postoperative fo llow-up showed that the percentage of patients with G3 resected tumors of the digestive tract, who had a mean level of anti-TF IgG above the cut- off value (1.53), was significantly higher than that of patients with G1 + G2 resected tumors (X2 = 3.89, all patients; X2 = 5.34, patients without regional lymph node metastases; P < 0.05). The percentage of patients with a tumor in stage I, whose mean anti-TF IgG level remained above the cut-off value (1.26), was significantly higher than that of patients with the cancer in stages Ⅲ-Ⅳ (X2 = 4.71, gastric cancer; X2 = 4.11, gastrointestinal cancer; P < 0.05). The correlation was observed to exist between the level of anti-TF IgG and the count of lymphocytes (r = 0.517, P < 0.01), as well as between the level of anti- Tn IgG and that of serum CA 19-9 (r = 0.481, P < 0.05). No positive delayed-type hypersensitivity reaction in skin test challenges with TF-PAA in any of the fifteen patients, including those with a high level of anti-TF IgG, was observed. CONCLUSION: The surgical operation raises the level of anti-carbohydrate IgG in most patients, especially in those with the G3 tumor of the gastrointestinal tract. The follow-up demonstrates that after surgery the low preoperative level of TF antibodies may be considerably increased in patients with the carcinoma in its early stage but remains low in its terminal stages. The stage- and morphology-dependent immunosuppression affects the TF-antibody response and may be one of the reasons for unresponsiveness to the immunization with TF-antigens.