Background-Angiotensin-converting enzyme (ACE) inhibition potentiates the tissue-type plasminogen activator (t-PA) response to exogenous bradykinin. This study tested the hypothesis that ACE inhibition increases endothelial t-PA release through endogenous bradykinin. Methods and Results-We measured the effect of intra-arterial enalaprilat (5 g/min) on forearm blood flow (FBF) and net t-PA release before and during intra-arterial infusion of bradykinin (25 to 400 ng/min) and methacholine (3.2 to 12.8 g/min) in 24 smokers pretreated with bradykinin receptor antagonist HOE 140 (100 g/kg intravenously) or vehicle.There was no specific effect of HOE 140 on FBF or forearm vascular resistance (FVR, 29.9Ϯ3.6 versus 29.7Ϯ3.6 mm Hg · mL Ϫ1 · min Ϫ1 · 100 mL Ϫ1 after vehicle and HOE 140, respectively, Pϭ0.956 between groups). Resting FVR decreased during enalaprilat compared with vehicle or HOE 140, but not compared with baseline, and the effect was similar in the 2 groups (22.0Ϯ2.7 and 24.1Ϯ2.9 mm Hg · mL Ϫ1 · min Ϫ1 · 100 mL