A. Estrogen receptor antagonist, ICI 182,780, was added to cultures 1h before treatment with 17β-estradiol. Estrogen effects on Tat-induced increased expression of Bax were reversed by ICI 182,780, suggesting that estrogenic actions on this protein are mediated by ER signaling. B. Estrogen effects on Bcl-2 expression were not attenuated by the addition of ER antagonist. C. Specific antagonists for ERα (MPP, 100nM) and ERβ (PHTPP, 100nM) were added to cultures 30 min before treatment with 17β-estradiol. ER subtype specific antagonists reveal that ERβ mediated signaling preferential for estrogen effects on Bax. Experiments performed in triplicate, *P<0.05 as compared to Tat-treated cultures, **P<0.05 compared to Tat+E treated cultures. Legend box: Tat (T), Tat+Estrogen (T/E), T/E+ICI182, 780 (T/E/I), T/E+ MPP (T/E/M), T/E+PHTPP (T/E/P). Reference line in graph represents control group.