The aim of this double-blind randomized study was to compare the antihypertensive effects of trandolapril and nitrendipine in the elderly. After a 2-week placebo period, patients received either trandolapril 0.5 mg or nitrendipine 10 mg, once daily for 15 days. At the end of this period, according to a forced titration, the dose was increased to 2 mg of trandolapril or 20 mg of nitrendipine once daily for 2 months. Seventy-three hypertensive patients, aged 65 and over, entered the study. Demographic data and initial blood pressure (BP) level were comparable in the two groups. The antihypertensive effect, measured with a mercury sphygmomanometer, was assessed in 64 patients: SBP decreased by 18.6 +/- 12.1 mm Hg in the trandolapril (P < 0.001) and by 21.0 +/- 13.7 mm Hg in the nitrendipine group (P < 0.001); DBP decreased by 13.4 +/- 8.5 mm Hg in the trandolapril group (P < 0.001) and by 15.4 +/-8.2 mm Hg in the nitrendipine group (P < 0.001). No statistically significant difference was seen between the two treatment groups. A sub-group of 42 patients were evaluated by 24 h ambulatory BP monitoring. Mean 24 h ambulatory SBP/DBP decreases were 6.6 +/- 18.0/8.4 +/- 8.5 mm Hg in the trandolapril group (P < 0.001) and 5.7 +/- 11.1/7.2 +/-9.6 mm Hg in the nitrendipine group (P < 0.001). The differences between the two treatment groups were not statistically significant. The antihypertensive action of trandolapril was sustained throughout the 24 h period with a trough-to-peak ratio of 70.2% for SBP and 70.9% for DBP. Nitrendipine exerted its action mainly during the day, with a very modest antihypertensive effect during the night and early morning; its trough/peak ratio was 25.9% for SBP and 28% for DBP. The tolerance of both treatments were good; seven patients were withdrawn from the trial for adverse events (four in the nitrendipine group, three in the trandolapril group).