ABSTRACT: The ascites fluids from 9 patients with invasive gynecologic neoplasms were examined to determine the immunocompetence of the mononuclear ascites cells and the immunoregulatory properties of the cell-free ascitic fluid. Blood mononuclear cells (from 5 patients) were also tested. The mononuclear cells from the cancer patients responded poorly to stimulation with polyclonal mitogens; only the blood mononuclear cell response to pokeweed mitogen was not significantly less than that of normal subjects. The addition of autologous serum or cell-free ascitic fluid to the cell cultures enhanced the response of the cells to phytohemagglutinin and pokeweed mitogen, had little effect on the response to concanavalin-A, and greatly depressed the response to succinyl-concanavalin-A. We found no evidence for the presence of suppressor cells in the ascites cell populations. The data are consistent with the thesis that the depressed immune responses are the result of malnutrition associated with advanced malignant disease.