Eighteen patients with a mean age of 54.7 years were included in the study. All patients had a diagnosis of mild or moderate essential hypertension (sitting diastolic blood pressure of 96 to 114 mm Hg). The study design was single blind and in two phases: phase I, placebo (4 weeks), and phase II, the active treatment (8 weeks) with increasing doses, if needed, of doxazosin every 2 weeks (1, 2, 4, and 8 mg/day). Results show that doxazosin has an antihypertensive effect that is dose dependent. Systolic, diastolic, and mean blood pressures were decreased significantly, and no effect on heart rate was observed. Doxazosin significantly inhibited the platelet aggregation induced by epinephrine, adenosine diphosphate, and collagen in a dose-dependent manner. In addition, treatment with doxazosin lowered total serum cholesterol and triglyceride levels, without changing other standard biochemical parameters. This indicates that doxazosin could offer a distinct therapeutic advantage in the modulation of atherogenic and thromboembolic factors associated with coronary heart disease.