 At present, there are two mechanisms of long-acting antihypertensive agents. One is that the compound itself has a long half life time and hence shows a long term effect. Another is that the efficacy of a short-acting drug is elongated by using a slow release or a controlled release such as GITS technique. However, the latter mechanism may vary between individuals because of the difference in the gastrointestinal function. Therefore, a long-acting compound should be more reliable in the maintenance of long term efficacy than slow release or controlled release agents. In the class of dihydropyridine calcium channel blockers, amlodipine is a long-acting compound because of a long half life time up to 50 hours, and nifedipine GITS uses a controlled release technique. Several recent studies compared 24-h blood pressure lowering effect of these 2 drugs, but produced inconsistent results. At least one study suggested that amlodipine may prevent morning blood pressure rise more effectively than nifedipine GITS. However, other studies demonstrated similar effect on morning blood pressure control of these 2 drugs. The inconsistency might be attributable to a chance finding, because of the small sample size less than 100. Therefore, a randomized controlled trial with a larger sample size is required to compare these 2 dihydropyridines in the blood pressure control over 24 hours in general and during early morning hours and at night in particular. 