Because studies have shown that 17beta-estradiol (E2) produces anti-inflammatory effects after various adverse circulatory conditions, we have recently demonstrated that E2 significantly reduced the acute lung injury. Moreover, previous results suggest that peroxisome proliferator-activated receptor-alpha (PPAR-alpha), an intracellular transcription factor activated by fatty acids, plays a role in the control of inflammation. With the aim to characterize the role of PPAR-alpha in estrogen-mediated anti-inflammatory activity, we tested the efficacy of E2 in an experimental model of lung inflammation, carrageenan-induced pleurisy, comparing ovariectomized wild-type (WT) and PPAR-alpha lacking (PPAR-alphaKO) mice. Results indicate that E2-mediated anti-inflammatory activity is weakened in PPAR-alphaKO mice, compared with WT control groups. In particular, E2 was less effective in PPAR-alphaKO, compared with WT mice, in inhibition of cell migration as well as lung injury, NF-kB activation, TNF-alpha production, and inducible nitric-oxide synthase (iNOS) activation. Moreover, macrophages from PPAR-alphaKO were less susceptible to E2-induced iNOS inhibition in vitro compared with macrophages from WT mice. Moreover, the results indicate that PPAR-alpha was required for estrogen receptor up-regulation, following E2 treatment. These results show for the first time that PPAR-alpha contributes to the anti-inflammatory activity of E2.