Antihypertensive monopharmacotherapy with diuretics renders blood pressure (BP) values under control in a large percentage of patients suffering from essential hypertension, and it reduces cardiovascular morbidity and mortality. Diuretics are effective in adult and elderly hypertensive subjects, independently of their race. Treatments with classic (high) doses of antihypertensive diuretics, such as 25 mg hydrochlorothiazide once daily, raise the activity of the RAA system, decrease plasma potassium and magnesium concentrations, and cause untoward changes in carbohydrate metabolism and in the plasma lipid profile. These changes appear to limit the positive response of cardiovascular prognosis to antihypertensive therapy with classic doses of diuretics. Lower doses of diuretics reduce high BP to the sought extent in many patients, and they do not elicit or cause only mild unfavourable neuroendocrine and metabolic changes. When a low dose of an antihypertensive diuretic substance is used as monopharmacotherapy, it may take 12-14 weeks after the initiation of treatment for BP to attain final stable values. The following low-dose oral formulations of diuretics constitute effective once-daily monopharmacotherapies for mild-to-moderate uncomplicated essential hypertension: bendrofluazide 1.25 mg, chlorthalidone 12.5 and 15 mg, cicletanine 50 mg, cyclopenthiazide 0.125 mg, HCTZ 12.5 mg, and torasemide 2.5 and 5 mg. These formulations are safer than classically used high-dose formulations such as hydrochlorothiazide 25 and 50 mg.