To examine the involvement of vascular tissue-specific signaling pathways in the pathophysiology of OHSS, in which the integrity of ovarian blood vessels is compromised by hCG, thereby resulting in fluid leakage and accumulation in the abdomen and sometimes the chest2,4, we focused our attention on one key protein from the VEGF signaling pathway (i.e., VEGF) and one from the Ang-Tie signaling pathway (i.e., Tie1). Here, ANG is linked to ovarian hyperstimulation syndrome.