The NFkappaB family of transcription factors, particularly the activated p50/p65 heterodimer, is expressed in vascular cells during intimal thickening formation when hemodynamic conditions are altered. Here, we report that p50, p65, IkappaBalpha and IKKalpha display different spatial and temporal patterns of expression and distribution during both chicken embryo aortic wall remodeling and intimal thickening development. Additionally, we show that both p50 and p65 were located in the nucleus of some mesenchymal cells expressing alpha-smooth muscle actin which are present in the spontaneous intimal thickening observed at embryonic days 12-14 of development. We also demonstrated that both NFkappaB subunits are present in monolayers of primary embryonic aortic endothelial cells attached to fibronectin and stimulated with complete medium. This study demonstrates for the first time the presence of activated NFkappaB during the remodeling of the embryonic aortic wall and the formation of intimal thickening, providing evidence that suggest a possible role for this transcription factor in the EndoMT process.