Endothelial barrier dysfunction is associated with the pathogenesis of a number of disorders in the body, but the aetiology is unclear. We have investigated the mechanism of the psychological stress mediator, corticotropin releasing hormone (CRH), on compromising the endothelial barrier function. Human endothelial cell line, Hmvec cells, was cultured in monolayers as a model of endothelial barrier. Human peripheral CD14+ cells were collected to be used as effector immune cells. The transepithelial resistance (TER) and permeability of horseradish peroxidase (HRP) were used as indicators of endothelial barrier function. Apoptosis in Hmvec cells were analysed by flow cytometry. Human CD14+ cells expressed both receptors (R) of CRH, the CRH-R1 and CRH-R2. Exposure to CRH induced CD14+ cells to release tumour necrosis factor (TNF)-α. CRH-activated CD14+ cells decreased TER and increased the permeability to HRP in co-cultured Hmvec monolayers. Co-culture with CRH-activated CD14+ cells increased the apoptosis in Hmvec cells. We conclude that CRH can activate CD14+ cells to produce TNF-α and compromise endothelial barrier function by inducing apoptosis of the endothelial cells.