Background: We have previously shown that 17-estradiol (E2) attenuates responses to endoluminal injury of the rat carotid artery, at least in part by decreasing inflammatory mediator expression and neutrophil infiltration into the injured vessel, with a major effect on the neutrophil specific chemokine cytokine-induced neutrophil chemoattractant (CINC)-2. Current studies tested the hypothesis that activated rat aortic smooth muscle cells (RASMCs) express these same inflammatory mediators and induce neutrophil migration in vitro, and that E2 inhibits these processes by an estrogen receptor (ER) dependent mechanism. Methods and Results: Quiescent RASMCs treated with E2, the ER-selective agonist propyl pyrazole triol (PPT), the ER-selective agonist diarylpropiolnitrile (DPN) or vehicle for 24 hrs were stimulated with tumor necrosis factor (TNF)- and processed for real-time RT-PCR, ELISA or chemotaxis assays 6 hrs later. TNF- stimulated and E2 attenuated mRNA expression of inflammatory mediators, including P-selectin, intercellular adhesion molecule (ICAM)-1, vascular cell adhesion molecule (VCAM)-1, monocyte chemoattractant protein (MCP)-1, and CINC-2. DPN dose-dependently attenuated TNF-α-induced mRNA expression of CINC-2, while PPT had no effect. The anti-inflammatory effects of DPN and E2 were blocked by the non-selective ER-inhibitor ICI 182,780. ELISA confirmed the TNF--induced increase and E2-induced inhibition of CINC-2 protein secretion. TNF- treatment of RASMCs produced a 2-fold increase in neutrophil chemotactic activity of conditioned media; E2 and DPN treatment markedly inhibited this effect. Conclusions: E2 inhibits activated RASMC pro-inflammatory mediator expression and neutrophil chemotactic activity through an ER-dependent mechanism.