This study was performed on anaesthetized male Wistar rats that received a continuous intravenous perfusion during 1.25 h of an aqueous extract of aerial parts of Urtica dioica L. (Urticaceae) at a low dose of 4 mg/kg/h or at a high dose of 24 mg/kg/h, or furosemide (control diuretic) at a dose of 2 mg/kg/h. As compared with a control period in each rat, the arterial blood pressure was reduced proportionally to the dose of the perfusion of the plant extract (15 and 38%, P<0.001, respectively). These effects were accompanied by a correlative increase of diuresis (11 and 84%, P<0. 001, respectively) and natriuresis (28 and 143%, P<0.001, respectively). In the rats perfused by furosemide, the arterial blood pressure was reduced by 28% (P<0.001). The diuresis and natriuresis were also increased proportionally in this case (85 and 155%, P<0.001, respectively). Nevertheless, the hypotensive action of U. dioica was reversible during the recovery periods in about 1 h with the lower dose of the plant extract and furosemide, while the effect of the higher dose was persistent, indicating a possible toxic effect. In conclusion, the results demonstrate an acute hypotensive action of U. dioica that indicates a direct effect on the cardiovascular system. Moreover, diuretic and natriuretic effects were also observed, suggesting an action on the renal function. Finally, the plant extract seems to have a toxic effect at the higher dose.