The adhesive force generated by the interaction of integrin receptors with extracellular matrix (ECM) at the focal adhesion complex may regulate endothelial cell shape, and thereby the endothelial barrier function. We studied the role of focal adhesion kinase (FAK) activated by integrin signalling in regulating cell shape using cultured human pulmonary artery endothelial cells. We used FAK antisense oligonucleotide (targeted to the 3'-untranslated region of FAK mRNA (5'-CTCTGGTTGATGGGATTG-3') to determine the role of FAK in the mechanism of thrombin-induced increase in endothelial permeability. Reduction in FAK expression by the antisense augmented the thrombin-induced decrease in transendothelial electrical resistance (decrease in mock transfected cells of -43 +/- 1 % and in sense-transfected cells of -40 +/- 4 %, compared to the decrease in antisense-transfected cells of -60 +/- 3 %). Reduction in FAK expression also prolonged the drop in electrical resistance and prevented the recovery seen in control endothelial cells. Thus, the thrombin-induced increase in permeability is both greater and attenuated in the absence of FAK expression. Inhibition of actin polymerization with latrunculin-A prevented the translocation of FAK to focal adhesion sites and tyrosine phosphorylation of FAK and paxillin, and concomitantly reduced the thrombin-induced decrease in electrical resistance by approximately 50 %. Thus, the modulatory role of FAK on endothelial barrier function is dependent on actin polymerization. FAK translocation to focal adhesion complex in endothelial cells guided by actin cables and the consequent activation of FAK-associated proteins serve to reverse the decrease in endothelial barrier function caused by inflammatory mediators such as thrombin.