This study was designed to assess the antihypertensive efficacy and overall tolerance of doxazosin in patients with mild-to-moderate essential hypertension. Doxazosin was administered in once-daily dose from 1 to 3mg to 97 patients both in a general hospital and a local clinic in rural area. These patients are composed of three groups. One group has 49 Patients treated with doxazosin monotherapy, another group with 31 patients treated with doxazosin as well as other antihypertensive drugs combined and a third group is composed of 17 patients with renal insufficiency n addition to hypertension. The patients in the third group with renal insufficiency had 2.5mg/dl-5.0mg/dl in serum creatinine. Results are as follows : 1) The study sample is composed of 37 males (38.1%) and 60 females (61.9%) with mean age 51.4 years. Among three subasmples no statistically significant difference is observed in age, sex, mean body weight and heigh at 0.05 error level. 2) A total of 47 patients (48.5%) of the 97 patients have completed twelve-week doxazosin antihypertensive treatment. At a mean dose of 4.4+/-0.4mg at twelfth week, 37 patients (78.7%) responded to doxazosin therapy. Twenty-nine(61.7% patients achieved "excellent" blood pressure control(mean sitting DBP of < or =90mmHg), and 8 patients (17.0%) showed "good respone" (10mmHg or more DBP reduction from baseline). Whereas remaining 10 patients (21.3%) showed only "fair response" (5-9mmHg DBP reduction) or "failed"(0-4mmHg DBP reduction). In doxazosin monotherapy group thirteen(68.4%) of nineteen patients showed "excellent" or "good response" at a mean dose of 4.8mg/day. Combination therapy group with eighteen patients showed 100% therapeutic success. This group had fourteen(77.8%) "excellent" and four(22.2%) "good respinse" at a mean daily dose of doxazosin 3.9mg. Renal insufficiency group with ten patients showed six(60.0%) "excellent" and four (40.0%) "failure"cases at a mean daily dose of 4.6mg. 3) The mean baseline sitting blood pressures of doxazosin monotherapy group were 175/109 whose blood pressure at twelfth week were 150/94 at a mean daily dose of 4.8mg. The baseline blood pressure of combined therapy group 180/111 were reduced to 145/91 at twelfth week at a mean daily dose of 3.9mg. Those of renal insufficiency group were 177/112 and 156/98 respectively at a mean doxazosin daily dose of 4.6mg. 4) Of the 97 study cases, adverse effect were reported in 19.6%. The most prevalent adverse effects were dizziness(11.3%), blurred vision(9.3%), headache(5.2%), most of which were mild or moderate and disappeared with or were tolerated on continued therapy. But three cases(3.1%) had to refrain from doxazosin administration due to blurred vision, dizzines, and headache. 5) The change of lipid analysis between before and after treatment in the monotherapy group with doxazosin showed 3.8% decrease of total cholesterol and 4.6% increase of HDL cholesterol and 11% increase of triglycerides, which were not statistically significant. In the combination therapy group 0.4% decrease of total cholesterol, 24.1% decrease of HDL cholesterol and 44.3% increase of triglycerides were observed. In the renal insufficiency group 4.9% decrease of total cholesterol, 22.1% decrease of HDL cholesterol, 0.1% decrease of triglycerides were observed. But all these findings have limitation in generalization due to small number of sample and a short period of observation. 6) Laboratory chemistry test results revealed no apparent treatment-related abnormalities.