Abstract: Angiotensin-Converting Enzyme (ACE) is a dipeptidyl carboxypeptidase (EC: 3.4.15.1) that catalyzes the conversion of angiotensin I to the potent vasoconstrictor angiotensin II. Angiotesin II is responsible for an increase in blood pressure and maintenance of hypertension through the stimulation of oxidative stress. The relationship between Coronary Artery Disease (CAD), Angiotensin-Converting Enzyme (ACE) activity, ascorbic acid and serum antioxidant status in patients with coronary artery disease. A group of 65 patients with angiographically defined Coronary Artery Disease (CAD) and 60 normal control subjects were examined. The activity of Angiotensin-Converting Enzyme (ACE) was determined by the reversed-phase High Performance Liquid Chromatography (HPLC) to separate and quantify Hippuryl-Histidyl-Leucin (HHL) and Hippuric Acid (HA). Ferric Reducing Ability of Plasma (FRAP Assay) as a measure of antioxidant power was used. Serum ascorbic acid concentration was determined photometrically. The results demonstrated significant differences in ACE activity, antioxidant and ascorbic acid between CAD cases and normal controls. Increased levels of ACE activity in serum have been related to coronary artery disease. Serum ascorbic acid concentration (25.6±3.8 mg dL-1) and total antioxidant capacity (475.5±18.51 μM L-1) were significantly (p<0.05) decreased in CAD patients compared with controls.