The antihypertensive effect of doxazosin 1-16 mg once-daily was compared with that of atenolol 50-100 mg once-daily, and placebo, utilizing a double-blind parallel group (12 patients each) design. Blood pressure (BP) and pulse rate were determined in out-patients who returned for clinic visits every 2 weeks for 14 weeks. During the first 4 weeks, all patients received single-blind placebo therapy. During the subsequent 10 weeks, patients were randomized to placebo, atenolol or doxazosin treatment. After 2 weeks of doxazosin therapy 16 mg daily, there was a significant decrease from baseline (single-blind placebo period) in supine diastolic BP (P less than 0.01) and standing diastolic BP (P less than 0.001). The decreases in supine and standing diastolic BPs in the doxazosin 16 mg daily group were significantly (P less than 0.01) different from the corresponding BPs of the placebo group. At weeks 12 and 14, heart rates in the doxazosin group were not significantly different from baseline or from those in the placebo group. After 4 and 6 weeks of atenolol 100 mg daily, there was a significant decrease from baseline in both supine (P less than 0.001 and P less than 0.05) and standing (P less than 0.05) diastolic BPs and heart rates (P less than 0.05). However, when the atenolol group was compared with the placebo group, a significant decrease occurred only with supine diastolic BP at week 12 (P less than 0.01) and not at week 14; but significant decreases occurred in supine and standing heart rates at weeks 12 and 14 (P less than 0.05).(ABSTRACT TRUNCATED AT 250 WORDS)