The role of prostaglandins (PG) has been evoked in the mechanism of action of indapamide. Indeed, PG can act in the regulation of the blood pressure (BP) at different levels: vasodilatation, diuretic, natriuretic, antagonism of angiotensin II and vasopressin (VP), action on adrenergic system. To confirm this hypothesis, we studied the action of certain eicosanoids inhibitors on the antihypertensive action of indapamide in the SHR rat, anaesthetized with pentobarbital (40 mg/kg i.p.). Indapamide (3 mg/kg i.p.) induces significant decrease on BP over 60 min. Mepacrine (5 mg/kg i.p.), phospholipase A2 inhibitor, indomethacin (5 mg/kg i.p), cyclo-oxygenase inhibitor, and tranylcypromine (0,1 mg/kg i.p.), prostacyclin synthase inhibitor, antagonize the antihypertensive action of indapamide. In order to eliminate the importance of VP, we used Brattleboro rats (genetically depleted in VP): indapamide (3 mg/kg i.p.) maintains its hypotensive activity. To eliminate the role of kidney in PG synthesis, we have used cyclo-oxygenase extrarenal inhibitor (sulindac) and the bilateral nephrectomy. Sulindac (1,25 mg/kg i.p.) and the bilateral nephrectomy do not remove the hypotensive action of indapamide. These results, demonstrating the PG extrarenal role and probably that of PGI2, localized in the vascular wall, could explain part of the antihypertensive mechanism of indapamide.