The pathogenesis of preeclampsia is not clear but the disease is characterised by systemic endothelial cell dysfunction that is considered to be triggered by a placental factor. Necrotic trophoblastic debris that is deported in the maternal blood is one possible placental trigger for preeclampsia. Syncytial knots were first associated with preeclampsia over 100 years ago. However, syncytial knots are very large and most are trapped in the pulmonary capillaries making it difficult to envisage how they could lead to widespread systemic endothelial cell dysfunction. This study was undertaken to examine whether conditioned medium from endothelial cells that have phagocytosed necrotic trophoblastic debris could adversely affect the proliferation or survival of fresh endothelial cells. Trophoblastic cellular debris, harvested from placental explants was added to endothelial cell monolayers directly or after induction of necrosis by freeze-thawing. Conditioned medium from the endothelial cell cultures was exposed to fresh endothelial cells and their proliferation measured by Alamar Blue, and CyQUANT®NF cell proliferation assays. Endothelial cell death was examined by a fluorogenic caspase-3 activity assay and LDH release. Conditioned medium from endothelial cells that had phagocytosed necrotic but not apoptotic trophoblastic debris significantly inhibited the proliferation of fresh endothelial cells but did not induce their death. The conditioned medium also reduced cell-surface endoglin expression by fresh endothelial cells. These results confirm that phagocytosis of necrotic trophoblastic debris by endothelial cells results in the secretion of soluble factors that might explain how necrotic trophoblastic debris trapped in the pulmonary capillaries could induce systemic endothelial cell dysfunction. © 2010 Elsevier Ltd. All rights reserved.