Ketanserin is a 5-HT2 receptor antagonist without partial agonist properties which also possesses weak alpha 1-adrenoceptor antagonistic activity, which may explain its antihypertensive mechanism of action in patients with essential hypertension. It also inhibits the effects of serotonin on platelets in cardiovascular disease, inhibits vasoconstriction caused by the amine, and when administered intravenously improves some haemorheological indices in patients with ischaemic diseases. The antihypertensive effect of oral ketanserin 40 mg twice daily is comparable with that of total daily doses of metoprolol 200 mg, propranolol 160 mg, captopril 100 mg, enalapril 20 mg, hydrochlorothiazide 50 mg, or alpha-methyldopa 1000 mg and is achieved without adverse effect on plasma lipoproteins or carbohydrate metabolism in patients with concomitant diabetes mellitus. Evidence from prospective studies suggests a greater antihypertensive efficacy in the elderly than in younger patients. In patients with intermittent claudication, results have been inconsistent in small studies, while a large study showed no improvement in pain-free walking distance but fewer amputations compared to placebo. In Raynaud's phenomenon symptomatic improvement relative to placebo was achieved in larger trials. Its role in preventing atherosclerotic complications requires further investigation. Ketanserin is reasonably well tolerated, the frequency of adverse effects being comparable with that of other antihypertensive drugs in controlled trials. Dizziness, tiredness, oedema, dry mouth and weight gain are the most commonly reported effects. Ketanserin prolongs QT interval in a dose-related manner, and when given in certain predisposing circumstances ventricular arrhythmias and syncope may occur. Administered intravenously, ketanserin 10mg followed by an infusion of 2 to 4 mg/h controls moderate to severe pre- and postoperative hypertension in most patients, acting as a balanced vasodilator, lowering cardiac pre- and afterload. Although the arrhythmogenic potential of ketanserin in patients receiving potassium-depleting diuretics requires suitable precautions, it appears that its antihypertensive activity is suited to the elderly provided plasma potassium concentrations are normal at the start of treatment and are maintained within the normal range.