Seventeen subjects with essential hypertension (14 men, 3 women, 40-69 years of age), 13 of whom continued their previous antihypertensive therapy, completed a double-blind crossover trial of ketanserin 40 mg twice daily versus placebo tablets twice daily. Each treatment phase was 6 weeks in duration. For the group as a whole, blood pressure (BP) was reduced in the ketanserin phase compared with the placebo phase: supine mean BP decrease: 4 +/- 1 mm Hg (p less than 0.05); standing mean BP decrease: 7 +/- 1 mm Hg (p less than 0.001). Heart rate (HR) was also significantly decreased in the ketanserin phase (5 +/- 1 beats/min) (p less than 0.001). When individual subgroups were analysed, the reductions in BP and HR were greater in subjects already receiving antihypertensive therapy, diuretics, and/or beta-adrenergic blockers. Changes were observed in 24-h urine sodium and potassium excretion: Sodium (mmol/day): placebo 137 +/- 17, ketanserin 174 +/- 19 (p less than 0.05); potassium (mmol/day): placebo 74 +/- 8, ketanserin 57 +/- 5. For the group as a whole, there were no significant adverse effects during the ketanserin phase, although two subjects had a dose reduction of ketanserin because of drowsiness and dizziness. Two additional subjects withdrew from the study owing to adverse effects, one in the placebo phase. In conclusion, ketanserin in the dose administered has a modest hypotensive effect, which is best seen in subjects already receiving other antihypertensive agents.