Peripheral blood lymphocyte subsets were studied in 70 patients who underwent gastrectomy for gastric carcinoma. Lymphocyte subsets were analysed before and after gastrectomy by use of monoclonal antibody for cell membrane markers. There were significant differences in the gastrectomized patients with splenectomy compared to the patients without splenectomy in postoperative changes of lymphocyte subsets as follows. Decrease of OKT4 and increase of OKT8. Temporary decrease of B-1. Continuous increase of Leu-7. These results suggest that gastrectomized patients with splenectomy show a decrease in helper activity, an increase of suppressor activity of T lymphocytes and a compensatory increase of population of natural killer cells in association with suppression of natural killer activity.