['The goal of this study was to determine whether the effect of L-arginine on endothelium-dependent vasodilation evoked with acetylcholine differs between the coronary and forearm vasculatures in humans.', 'Administration of L-arginine, a substrate in the production of endothelium-derived nitric oxide, may stimulate the release of nitric oxide.', 'Seven patients with normal coronary angiograms and seven with mild coronary artery disease and hypertension underwent coronary arteriography and an intracoronary Doppler catheter technique, and the diameter of the large epicardial coronary artery and coronary blood flow were measured. Forearm blood flow was measured by use of a strain gauge plethysmograph.', 'Before L-arginine administration, acetylcholine (1 to 30 micrograms/min) increased coronary blood flow with modest vasoconstriction of a large coronary artery. Acetylcholine (4 to 24 micrograms/min) also increased forearm blood flow. The acetylcholine-induced increases in coronary and forearm blood flow were significantly less in patients with coronary artery disease than in control patients. Intracoronary infusion of L-arginine at 50 mg/min did not alter responses of the large coronary artery diameter or coronary blood flow to acetylcholine in either group. In contrast, L-arginine at 10 mg/min significantly (p < 0.01) augmented the forearm blood flow response to acetylcholine (4 to 24 micrograms/min) to a similar extent in the two groups.'] Does effect of L-arginine on acetylcholine-induced endothelium-dependent vasodilation differ between the coronary and forearm vasculatures in humans?