This is an open non-comparative study to evaluate the efficacy and tolerability of doxazosin mesilate in 540 subjects with either history or newly diagnosed mild/moderate hypertension. In all adult subjects of both sexes enrolled in this study, the diastolic blood pressure (DBP) was in the range of 95-115 mmHg at two different measurements both in clino- and orthostatism, in the absence of any heart pathology. Those patients who, after one-week wash-out period, reported DPB > or = 95 mmHg, were given doxazosin as a single daily dose. The initial dosage was 1 mg for three days; afterwards, patients have been instructed to take a whole 2 mg tablet in the morning up to the following visit (i.e. 14 days after the first administration). In case < or = 90 mmHg DBP control could not be obtained, the dosage has been increased to 4 mg and if after the same interval of time (i.e. 14 days) DPB control could not be achieved, the dosage was increased up to 8 mg (2 x 4 mg tablets) and/or the concomitant administration of another antihypertensive drug was instituted. At the beginning and at the end of the study blood collection for lipid profile determinations (total cholesterol, HDL cholesterol, LDL cholesterol, triglycerides), routine tests and complete urinalysis were performed. The onset of side-effects was reported in 84 (15.5%) subjects and only 13 (2.4%) of them had to discontinue the therapy. A comparative analysis of the incidence of side-effects between the total number of patients and those aged > or = 65 yrs. has not shown a significant difference. At week 24, a total of 540 subjects had completed the treatment. BP value normalization has been achieved with a mean dosage of 3.1 +/- 1.2 mg/day of doxazosin. Doxazosin administration did not produce clinically significant effects on heart rate. Laboratory data have evidenced a statistically significant increase in HDL cholesterol (p < 0.0001) and a significant reduction of mean values of total cholesterol, LDL cholesterol and triglycerides (p < 0.0001) at week 24, with respect to baseline. In the group of patients aged > or = 65 yrs. (116 patients) only a delta/percentage variation of HDL cholesterol with respect to baseline has been evidenced, after 24 weeks of treatment.