This study investigated whether angiotensin II AT 1-receptor blockade with losartan inhibits endothelium-monocyte interactions originating from long-term activation of the renin-angiotensin system in hypertensive transgenic rats [TGR (mRen2) 27]. The number of circulating activated monocytes, monocytes adhered to thoracic aorta endothelium, and the extent of endothelial cell injury were compared in adult male transgenic (mRen2) 27 and age-matched Hannover Sprague-Dawley (SD) rats after 12 days of continuous subcutaneous administration of saline (120 μl/24 h), losartan (10 mg/kg/24 h), or the vasodilator hydralazine (3 mg/kg/24 h). At the doses administered in this experiment, both losartan and hydralazine normalized mRen2 rat blood pressures equal to values in similarly treated SD rats. Compared with saline infusion, administration of either antihypertensive in mRen2 rats reduced (p< 0.05) endothelial cell injury, but only losartan significantly (p< 0.05) decreased the number of activated circulating and endothelium-adherent monocytes. Infusion of antihypertensives in SD rats had no effect on blood pressures, monocyte activity, or endothelial injury compared with saline administration. These findings suggest that the recruitment and infiltration of leukocytes into the subendothelium associated with renin-angiotensin system-induced hypertension is partly mediated by pressure-independent AT 1-receptor pathways.