Surgical brain injury causes neovascularization in the disrupted brain parenchyma, which occurs with the participation of endothelial-like cells. Differentiation of angioblasts from embryonic mesothelial cells has been proposed on the ground of biochemical and antigenic similarities between mesothelial and endothelial cells. Therefore, a transient localization of cytokeratin, the main mesothelial intermediate filament protein, to some embryonic vessels and endothelial progenitors, prompted us to use it to identify the source of cells participating in vessel formation after surgical brain injury. To determine the immunophenotypes of immature endothelial cells involved in new vessel formation following surgical rat brain injury, we used immunohistochemical and electron microscopic immunocytochemical techniques. Subcellular localization of protein markers: Flk-1, cytokeratin, and vimentin was examined in the cells investigated. Our results confirmed the existence of a diversity of immunophenotypes of immature endothelial cells in case of surgical-related brain injury.