The purpose of this study was to evaluate the effects of the alpha 1-blocking agent terazosin on blood pressure (BP) and blood lipids in a large, variant population of patients with hypertension. A total of 16,917 patients with hypertension were evaluated at 2214 primary and community care facilities; 7808 of these patients had not been treated previously for hypertension; 3928 were switched to terazosin from another antihypertensive agent; and 5181 received terazosin in addition to an agent that had not controlled their hypertension. Terazosin produced highly significant reductions in systolic (-18.2 +/- 0.2 mm Hg) and diastolic (-13.2 +/- 0.1 mm Hg) BP when used as monotherapy (mean dose, 3.1 mg; range, 2 to 10 mg) without causing a significant increase in heart rate. Equal antihypertensive efficacy was demonstrated in men, women, blacks, and whites of all ages, with particular benefit to elderly patients (> or = 65 years of age) with systolic hypertension. Comparative studies indicated that terazosin had equal antihypertensive efficacy in combination with diuretics, beta-blockers, calcium channel blockers, and angiotensin-converting enzyme (ACE) inhibitors. Patients who had not responded to monotherapy with one of these classes of antihypertensive drugs showed significant reductions of BP after terazosin, in the following average doses, was added to diuretics, 3.1 mg; beta-blockers, 3.4 mg; calcium channel blockers, 3.3 mg; and ACE inhibitors, 3.4 mg. Terazosin produced highly significant reductions in blood levels of total cholesterol (-5.0%), triglycerides (-6.1%), and low-density lipoprotein cholesterol (-7.6%) without change in high-density lipoprotein cholesterol when used as monotherapy. Similar favorable effects on blood lipid levels were demonstrated when terazosin was used in combination with all other classes of antihypertensive drugs. The greatest reductions in blood cholesterol (-9.2%) were observed among patients with hyperlipidemia (total cholesterol > or = 240 mg/dL). Terazosin maintained its antihypertensive efficacy and was well tolerated by patients with a variety of concomitant diseases, including congestive heart failure, peripheral vascular disease, chronic obstructive pulmonary disease, benign prostatic hyperplasia, diabetes, and obesity. Adverse effects occurred in 17.9% of patients and caused 2.2% to drop out of the study. The most frequent adverse effects were dizziness (4.8%), headache (2.5%), and asthenia (2.4%). Only 0.4% suffered syncope and 0.2% impotence. These data demonstrate the usefulness of terazosin as monotherapy or add-on therapy for treatment of hypertension.(ABSTRACT TRUNCATED AT 250 WORDS)