The activation status of T lymphocytes and the presence of various cytokines in ascitic fluid were examined to test peritoneal immunity in women with ovarian malignancies. Peripheral blood and peritoneal fluid were collected from 12 patients with primary ovarian cancer with ascites and 27 normal control subjects during laparoscopic examination. Lymphocyte subpopulations and the expression of activation markers on T lymphocytes were analyzed by dual-color flow cytometry. The concentrations of various cytokines and soluble interleukin (IL)-2 receptor-alpha were measured. CD8 T lymphocytes were the main component of peritoneal lymphocytes. CD69 and HLA-DR, but not CD25, were highly expressed on peritoneal T lymphocytes compared to those in peripheral blood. In ascitic fluid of ovarian malignancies, CD4 T lymphocyte concentrations were further decreased, resulting in a decreased CD4/CD8 ratio. Decreased expression of CD69 and CD25 was also noted on T lymphocytes from ascites compared with T lymphocytes in normal peritoneal fluid. IL-1b, tumor necrosis factor-alpha, IL-6, and soluble IL-2 receptor-alpha concentrations were increased significantly in the ascitic fluid of women with ovarian cancer. The decrease in activation markers on T lymphocytes is suggestive of an immunosuppressive state, despite the presence of abundant stimulatory cytokines. The immunosuppression may be multifactorial, attributed, in part, to the increased concentrations of soluble IL-2 receptor-alpha and other inhibitors.