The new orally active angiotensin II (A II) type-1 receptor antagonist olmesartan medoxomil is a prodrug, which is rapidly converted in vivo to the active metabolite, olmesartan. The pharmacology, antihypertensive efficacy and safety of olmesartan medoxomil and/or the pharmacologically active metabolite, olmesartan, have been evaluated in both non-clinical and clinical models. Orally administered olmesartan medoxomil is rapidly absorbed from the gastrointestinal tract and converted during absorption to olmesartan, which is subsequently excreted without further metabolism. Peak plasma concentrations of olmesartan occur 1-3 h after administration, after which concentrations decrease with an elimination half-life of 10-15 h. The absolute bioavailability of olmesartan from olmesartan medoxomil tablets is 28.6%. In a single-dose crossover study in 16 patients with mild-to-moderate hypertension receiving a sodium-restricted diet, statistically significant lowering of mean 24-h blood pressure was seen at doses of 10-80 mg. Evaluation of 14 phase II/III studies has confirmed the antihypertensive efficacy of olmesartan medoxomil in over 3500 patients who received the drug for up to 2 years. Frequencies of adverse events during treatment with olmesartan medoxomil and placebo are similar, with no evidence of a dose response. There are no clinically significant effects on laboratory parameters, and the drug-interaction potential of olmesartan medoxomil is low. Current indications are that olmesartan medoxomil is a true once-daily, orally active A II antagonist with good antihypertensive efficacy and a favourable adverse-event profile. Clinical pharmaco- dynamic and efficacy studies support a usual dose of 20 mg once daily, increasing to 40 mg if needed.