These undiagnosed pleural effusions are important clinical problem, so scientists spent much effort and time in searching for a new parameter to help in the diagnosis of etiology of different types of pleural effusions Vascular endothelial growth factor (VEGF) is a multifunctional cytokine that increases microvascular permeability and directly induces endothelial cell growth and angiogenesis. It was reported that it enhances the activation and migration of monocytes through the Fms- like tyrosine kinase (FLT) receptor of VEGF.