To obtain information regarding the immunologic capacity of uninvolved regional lymph nodes (RLNs) draining tumor, the in vitro response of regional lymph node cells (RLNCs) to PHA was investigated in lymph nodes from 55 patients with gastric or colorectal cancer, and gastric ulcer. Evaluation of data relative to cancer progress demonstrated that, in gastric cancer patients, the response of stimulated RLNCs from patients with middle stage carcinoma was significantly higher compared with those of cells from patients with early or late stage carcinoma, such being similar to the response of RLNCs from control patients with gastric ulcer. The results from colorectal cancer patients were also similar to those from patients with gastric cancer. Our results suggest that RLNs without metastasis contain cells capable of responding to PHA despite the presence of growing tumors in these cancer patients. In the results of PHA stimulation in relation to the lymph node morphology, we observed in both groups of patients with gastric or colorectal cancer that, regardless of the extent of the cancer lymph nodes with lymphocyte predominance there was a high PHA response while lymph nodes with lymphocyte depletion and unstimulated nodes exhibited a low PHA response. These results show a close relationship between this lymph node morphology and immunologic status of nodes.