Immune competent cells of regional lymph nodes in colorectal cancer patients: I. Flow cytometric analysis of lymphocyte subpopulation. Lymphocyte subpopulations of the regional lymph nodes in 20 colorectal cancer patients were measured by flow cytometry to analyze nodal lymphocytes phenotypically. Eleven patients with cholelithiasis were used as controls. Comparison of lymphocyte subpopulations between colorectal cancer and control groups revealed a significantly increased rate of Leu-12+ cells in the cancer patients. Furthermore, a significant increase of Leu-3a+ Leu-8- cells and a significant decrease of Leu-3a+ Leu-8+ cells were also found in the paracolic nodes of the cancer patients. However, Leu-2a+ Leu-15- cells were not different between the both groups. Meanwhile, in the cancer patients, the rates of Leu-4+, Leu-3a+, and Leu-3a+ Leu-8- cells were higher in the paracolic nodes compared with the intermediate nodes. Additional investigation of the correlation between clinicopathological features of the tumors and lymphocyte subpopulations, showed that Leu-12+ cells were related to the tumor size and Leu-2a+ 15- cells related to the histopathological type. The foregoing results indicate that the rates of both B and helper T cells, which may specifically participate in the antibody production, increase in the regional lymph nodes of colorectal cancer patients. 