Bay e 5009 (nitrendipine) is a new calcium-antagonist that acts mainly on blood vessel smooth muscles. The effects of this drug on hypertensive patients of both sexes was investigated. Nine patients were treated for 42 days at a fixed dosage of 1 tablet/day. A highly significant fall in arterial pressure was obtained (p less than 0.001). Seven patients took 20 mg/day of nitrendipine for 14 days and a significant reduction in A.P. was obtained (p less than 0.001): for the next four weeks, the dosage was increased to 20 mg twice a day when a further decrease in systolic and diastolic A.P. was obtained without the occurrence of side effects. A further five patients were treated for 14 day (20 mg/day). These showed a fall in blood pressure levels (p less than 0.001) but suffered from slight oedema which made it necessary to suspend the treatment. An increase in heart rate was noted in all patients (p less than 0.001). This was due to reflex adrenergic activation. Nitrendipine therefore proved effective as an antihypertensive drug even at a daily dose of only 20 mg.