Doxazosin, a selective alpha 1-inhibitor, was assessed in 34 patients with mild and moderate hypertension. This study involved three phases: (1) a 2-week baseline period, (2) an 8-week period in which patients received 1 to 8 mg of doxazosin once daily, and (3) a 4-week maintenance period. After 12 weeks, 77% of the efficacy evaluable patients were considered therapy successes (sitting diastolic blood pressure either less than or equal to 90 mm Hg with greater than or equal to 5 mm Hg reduction or greater than or equal to 10 mm Hg reduction) at a mean daily dose of 4.3 mg. Sixty-one percent achieved blood pressure control (sitting diastolic blood pressure less than or equal to 90 mm Hg) at a mean dose of 3.7 mg once daily. By the final treatment visit, systolic/diastolic blood pressures of efficacy evaluable patients were reduced by 17/12 and 17/11 mm Hg from a mean baseline of 160/100 and 156/101 mm Hg in the sitting and standing positions, respectively (p less than 0.05). Of the 34 patients, nine (26%) reported 12 adverse experiences, of which only one was severe. No clinically significant laboratory changes were apparent, and no trends were observed with regard to organ systems or correlations with dose or duration of treatment. The investigator's global assessment of efficacy of once-daily doxazosin therapy was excellent or good for 85% of patients and fair for 15% of patients. The investigator's global assessment of toleration was excellent or good for 91% of patients and fair for 9% of patients. The overall lipid profile indicated a decrease in total cholesterol and triglycerides.(ABSTRACT TRUNCATED AT 250 WORDS)