1. The aim of the present study was to compare the efficacy of nifedipine Oros and felodipine extended release (ER) in controlling 24 h ambulatory blood pressures (ABP) in hypertensive patients. 2. The study was a randomized cross-over design with a 2 week open placebo run-in phase and two observer-blind treatment periods. 3. Subjects were males and females, aged between 18 and 65 years, suffering from mild to moderate essential hypertension with a sitting mean diastolic blood pressure (DBP) within the range of 95-114 mmHg. Twenty-three subjects were randomized to treatment; 15 patients completed the study. 4. Treatment intervention was 2 weeks of placebo followed by either 30 mg nifedipine OROS once daily or 5 mg felodipine ER once daily for 6 weeks, which was titrated up to 60 mg nifedipine OROS daily or 10 mg felodipine ER daily after 2 weeks of treatment on the lower doses if the DBP was > 90 mmHg. The main outcome measure was 24 h ABP after 6 weeks of active treatment, evaluated by an independent observer blinded as to treatment allocation. 5. Compared with placebo, mean (+/- SD) 24 h DBP was reduced by 6.2 +/- 6.8 and 5.2 +/- 5.1 mmHg after nifedipine and felodipine, respectively. The 24 h mean systolic blood pressure (SBP) fell by 11.8 +/- 10.9 and 10.1 +/- 8.2 mmHg for nifedipine and felodipine, respectively, compared with placebo. There were no significant differences between the two active treatments in the reduction of DBP or SBP during the 24 h period, daytime or night-time. 6. Similar antihypertensive effects are achieved with nifedipine Oros and felodipine ER when doses are individually titrated, with no significant differences between the two treatments.