The aim of the study was to compare antihypertensive efficacy and safety of ketanserin with those of enalapril in the treatment of hypertension. The study design was controlled, cross-over, with randomized sequences. The efficacy was evaluated from data of 19 (9 males, 10 females) mean age 59.5 +/- 10.1 years, weight kg 68 +/- 12.1 with hypertension lasting over 5 years. Posology was ketanserin 20-40 mg bid, and enalapril 10-20 mg bid; both for three weeks. The efficacy was good with both treatments and the effects similar. In fact, at the end of the treatment with ketanserin, supine SBP was decreased 10 +/- 20 and DBP 5 +/- 10 mmHg, standing SBP was reduced 15 +/- 19 and DBP 7 +/- 15 mmHg. With enalapril supine SBP decreased 25 +/- 16 and DBP 10 +/- 13 mmHg, standing SBP was reduced 16 +/- 19 and DBP 8 +/- 18 mmHg. Changes of heart rate by either treatment were of no clinical importance. The safety of treatment with ketanserin was excellent, while 14.3% of the patients treated with enalapril had undesirable effects.