This study was designed to compare the efficacy and tolerability of amlodipine (AML) and ramipril (RAM) administered once a day in patients affected by mild to moderate primary systemic hypertension. Twenty outpatients, 12 men and 8 women (age range 35-64 years), were enrolled. The patients received single-blind placebo for 2 weeks and thereafter in a double-blind, randomized crossover sequence AML (10 mg) and RAM (5 mg), both for 4 weeks. At the end of each period, the patients underwent 24-hour noninvasive blood pressure monitoring with readings taken every 10 min during daytime (from 07.00 to 23.00 h) and 20 min during nighttime (from 23.00 to 07.00 h). Both AML and RAM induced a highly significant (p < 0.0001) decrease in blood pressure from 162/103 +/- 7/3 to 132/82 +/- 6/6 and 135/83 +/- 6/5 mm Hg, respectively. The mean blood pressure decreased from 122 +/- 5 to 99 +/- 6 (AML; p < 0.0001) and 100 +/- 5 mm Hg (RAM; p < 0.0001). No significant differences in heart rate were noted during drug administrations. Treatment did not have to be discontinued in any patient because of adverse reactions. In conclusion, both AML and RAM reduced the blood pressure markedly, even if AML proved to be significantly more effective than RAM.