Effect of beraprost sodium (BPS), a long-acting and orally active stable analogue of PGI2, on the macromolecular permeability of cultured vascular endothelial cells (HUVEC) was detected by the transport of FITC-albumin. Thrombin treatment resulted in induction of FITC-albumin transport across the endothelial cell monolayer. The albumin transport induced by thrombin was not accompanied by any damage to the cells. BPS had no effect on the permeability of resting endothelial monolayers, while BPS inhibited the thrombin-induced increase in the albumin permeability in a dose-dependent manner (30-1000 nM). Treatment of the cells with PGI2 or dibutyryl cAMP caused a significant inhibition of the thrombin-induced increase in the albumin permeability. These results strongly suggested that BPS suppressed the thrombin-induced macromolecular permeability in HUVEC through the elevation of its intracellular cAMP, and that BPS was a suppressor against inflammatory vascular changes such as exudation.