A long-term study of doxazosin in the treatment of mild or moderate essential hypertension in general medical practice. This study assessed the long-term (54 weeks) antihypertensive efficacy and safety of doxazosin in the treatment of mild or moderate essential hypertension, defined as sitting and standing diastolic blood pressure of 95 to 114 mm Hg. Of the 153 patients who successfully completed an initial 14-week trial, 61 continued uninterrupted into a 40-week extension study. Optimal antihypertensive efficacy was achieved by week 12 and maintained in all patients for the duration of 1 year. The final mean sitting blood pressure was 148/84 mm Hg and was reduced from a mean baseline level of 173/102 mm Hg. Occasional decreases in heart rate were observed, but these were not considered to be clinically relevant (1 to 3 beats/min). The mean final dose of doxazosin for patients evaluable for efficacy was 2.4 mg/day; 91.7% of patients were taking less than or equal to 4 mg/day. No increase in daily maintenance dose was observed from the initial phase to the long-term extension study. After 1 year of treatment, 93.3% of patients were considered a therapeutic success (sitting diastolic blood pressure greater than or equal to 10 mm Hg reduction from baseline or less than or equal to 90 mm Hg with greater than or equal to 5 mm Hg reduction). In no patients was there a worsening in the severity category of the hypertension. Total serum cholesterol concentrations were reduced significantly (6.6% p = 0.03) at the end of week 14. Reductions in total serum cholesterol levels persisted throughout the extension study, with a final reduction of 5.4%. 