The ability of estradiol (E2) to modulate the secretion of cytokines by CD4+ T cells was investigated using neuroantigen-specific T cell clones isolated from normal control subjects and patients with the demyelinating disease, multiple sclerosis. In the presence of E2, the majority of the tested clones showed a dose-dependent enhancement of Ag-stimulated IL-10 secretion. The secretion of IFN-gamma was also enhanced, although the peak enhancement occurred at lower E2 concentrations and at lower magnitude than observed for IL-10. By contrast, the effect of E2 on Ag-stimulated secretion of TNF-alphabeta was biphasic, with enhancement occurring at low doses, and inhibition present at high concentrations. E2 had no effect on the secretion of IL-4 or TGF-beta. These data indicate that E2 is capable of modulating both pro- and anti-inflammatory activities of CD4+ T cells and thus has the potential to influence the outcome of CD4+ T cell-mediated immune responsiveness.