Placental growth factor (PlGF) is a member of the vascular endothelial growth factor (VEGF) family of cytokines, which play important roles in the development and growth of the vascular or lymphatic endothelia. PlGF is secreted as a homodimer, but may also form PlGF/VEGF heterodimers and can synergistically enhance VEGF-induced angiogenesis and vascular permeability. While PlGF is expressed mainly in placental trophoblast during pregnancy, it is also expressed in various cell types including vascular cells, fibroblasts, leukocytes, hepatocytes, bone marrow-derived cells, neurons, epithelial cells and tumor cells. Serum levels of PlGF peak during pregnancy at weeks 26 – 28, and low serum PlGF is associated with the development of preeclampsia later in pregnancy. PlGF is a potential prognostic marker for tumor progression in several types of cancer, including renal, colorectal, gastric, breast, and lung. PlGF also plays a role in inflammatory conditions such as artherosclerosis and rheumatoid arthritis, where measurement of serum levels can enhance biomarker analysis of disease progression. In addition, PlGF is elevated in individuals with Sickle Cell Disease (SCD) and thought to play a role in the pathophysiology of pulmonary hypertension in patients with SCD.