A total of 713 patients with hypertension were evaluated in eight randomized, double-blind, placebo-controlled trials of terazosin administered in single daily doses ranging from 1 to 40 mg. In three of these studies, terazosin or placebo was added to ongoing antihypertensive drug therapy. Patient response was categorized (from excellent to inadequate) according to the change in supine diastolic blood pressure from baseline and the value at the final visit. The distribution of patients in these response categories differed significantly between patients treated with terazosin and those treated with placebo. Overall, 52 percent of terazosin-treated patients in these eight studies, compared with 30 percent of placebo-treated patients, had good to excellent responses. Subgroup analysis revealed that blood pressure response was not dependent on sex or age, although white patients appeared to achieve better responses to terazosin in comparison with placebo than did black patients. These studies demonstrate that terazosin administered once daily, either as monotherapy or in combination with other antihypertensive agents, effectively controls blood pressure in patients with mild to moderate hypertension.