Recent studies in rodents and in human in vitro systems suggest that the action of estrogen on bone is modulated by various bone-resorbing cytokines produced by osteoblasts, bone marrow cells, or both, but results among studies have been conflicting. Thus, we studied 20 untreated women (controls) and 20 women who had received estrogen replacement therapy since the time of menopause; both groups were 5 +/- 1 yr (mean +/- SE) postmenopausal. From bone marrow aspirates, we obtained marrow plasma to evaluate the production of cytokines by marrow and trabecular bone cells in vivo and marrow mononuclear cells to assess in vitro the constitutive and lipopolysaccharide-stimulated production of cytokines and also to test the in vitro effects of 17 beta-estradiol (10(-8) mol/L). Interleukin-1 alpha (IL-1 alpha), IL-1 beta, IL-6, IL-1 receptor antagonist, and IL-6-soluble receptor were measured by specific enzyme-linked immunosorbent assay. No statistically significant difference between the two groups in the level of any of these cytokines was detected in the bone marrow plasma or the conditioned medium in vitro. Furthermore, in vitro treatment with 17 beta-estradiol did not affect basal or lipopolysaccharide-stimulated cytokine production. Thus, our data suggest that for normal post-menopausal women, mediation of the effects of estrogen by a single cytokine is unlikely. Either multiple cytokines are involved and small changes in these are difficult to detect in clinical investigative studies, or other mechanisms are operative.