Understanding precisely immunocompetence, especially cell-mediated immunocompetence, is important for applying the proper immunotherapy. A tumor specific antigen (TSA), which is considered to be on cancer cells, but not on normal cells, causes an immunoreaction with the cancer bearing host. To detect TSA of gastric and colon cancer, we performed autologous skin tests on 28 gastric cancer and 25 colon cancer patients using a solution prepared from the mixed culture of tumor antigen extracted by deoxycholate (DOC) and autologous peripheral lymphocytes. There were 19 (67.9%) positive reactions among gastric cancer cases and 13 (52.0%) among colon cancer cases. The skin test used in this study showed a higher positive rate than the usual skin test using tumor extracts only. The skin test did not correlate with the clinical stage in gastric cancer cases, but in colon cancer patients in the late stage there was a low percentage of positive reactions. As for histological classification, cancer patients with tubular adenocarcinoma, signet-ring cell carcinoma and malignant lymphoma of the stomach had a high percentage of positive reactions to this skin test. Cancer patients with moderately differentiated adenocarcinoma of the colon had a tendency to have a slightly high positive rate. This skin test did not correlate with the serum CEA level and PPD skin test, which is a nonspecific skin test.