The anti-hypertensive efficacy and safety of extended-release (ER) felodipine (5, 10 or 20 mg) and amlodipine (5 or 10 mg) once daily were compared in patients with mild-to-moderate essential hypertension in a double-blind, double-dummy, randomised, comparative study. A total of 118 patients were allocated to a 12-week, double-blind treatment with either felodipine ER (n = 57) or amlodipine (n = 61). The anti-hypertensive effect was evaluated by measuring office blood pressure (BP) at baseline and after 4, 6, 8 and 12 weeks, together with 24 h ambulatory blood pressure monitoring (ABPM) at baseline, on day 1 of treatment and at the end of the study. The mean office BP changes from baseline to week 12 were -13.4 (+/- 15.7)/-11.8 (+/- 6.9) mmHg for felodipine ER (mean daily dose 11.2 mg) and -15.3 (+/- 17.0)/-12.9 (+/- 7.3) mm Hg for amlodipine (mean daily dose 7.4 mg). All BP reductions were significant (P < 0.01) with respect to time, but differences between treatment groups were not significant. The mean ambulatory BP changes from baseline to end of the study were -11.6 (+/- 5.2)/-10.0 (+/- 2.0) mmHg for felodipine ER and -16.3 (+/- 4.4)/-9.6 (+/- 3.0) mm Hg for amlodipine, both significant (P < 0.01). The fall in ambulatory SBP was significantly greater (P < 0.001) in the patients treated with amlodipine compared with felodipine ER whereas there was no difference between the groups with respect to ambulatory DBP. Both drgs were well tolerated with a withdrawl rate of 12% equally distributed.(ABSTRACT TRUNCATED AT 250 WORDS)