In a double-blind multicenter study, the new alpha 1-adrenoceptor inhibitor doxazosin was compared with atenolol for efficacy, safety and effect on serum lipids. One hundred and twenty-six patients with mild to moderate hypertension were randomly assigned to receive either doxazosin (n = 63) or atenolol (n = 63). The mean final dosages, administered once daily, to obtain 24-hour blood pressure (BP) control were doxazosin 12 mg (range 1 to 16) and atenolol 91.8 mg (range 50 to 100). Of 12 doxazosin and 7 atenolol patient withdrawals from the study, 7 doxazosin and 4 atenolol patients withdrew for treatment-related reasons. No statistically significant differences between treatment groups were found after 20 weeks in changes from baseline in standing and sitting BPs measured 24 hours after administration. Sitting BP (systolic/diastolic) was reduced by 10.5/9.8 mm Hg after doxazosin treatment and by 10.9/10.7 mm Hg after atenolol therapy. Standing BP was reduced by 8.8/7.7 mm Hg after doxazosin administration and 9.7/9.3 mm Hg after treatment with atenolol. Supine BP was measured in a small cohort of the study population, and doxazosin had a smaller effect than atenolol. After 20 weeks of treatment, both drugs reduced heart rate with atenolol producing a statistically significantly greater decrease than doxazosin (standing, doxazosin 5 beats/min, atenolol 16.2 beats/min, p less than 0.001; sitting, doxazosin 5 beats/min, atenolol 13.1 beats/min, p less than 0.001). Side effects were reported by 37 patients receiving doxazosin therapy and 34 patients receiving atenolol therapy.(ABSTRACT TRUNCATED AT 250 WORDS)