The antihypertensive efficacy and pharmacokinetics of a single 1 mg oral dose of doxazosin were investigated in five healthy male volunteers, six patients with renal failure not on hemodialysis, and four patients with end-stage renal failure studied between two hemodialyses. The dialyzability of doxazosin was studied in five patients. The maximum fall in blood pressure of both volunteers and patients occurred between 4 and 8 hours. In four of five volunteers the blood pressure had returned to baseline within 10 to 12 hours, whereas in the patients with renal failure it took as long as 72 hours. Maximum plasma concentrations were reached in 2.6 to 3.6 hours. The mean AUC did not differ significantly between the groups. The mean (SE) elimination t1/2 was 12.6 hours (3.3) in the volunteers and 13.3 hours (1.8) in the patients with renal insufficiency (not significant). Doxazosin was not appreciably dialyzable.