We report on alterations in IL-2 production and cell proliferation following PHA stimulation of peripheral blood lymphocytes (PBL) from stage-I endometrial carcinoma (EC) patients, and on mechanisms involved in these alterations. Our study includes 3 groups: EC patients, post-menopausal women at high risk of developing EC, and age-matched healthy women. IL-2 production was markedly lower in most EC patients than in healthy controls. Varying levels of IL-2 were produced by PBL from women in the high-risk group. The proliferative response of PBL to PHA appeared to correlate with levels of IL-2 production. Our results suggest that macrophages are involved, in part, in the modulation of T-cell functions of EC patients.