This study attempted to evaluate the efficacy of several "long-acting" antihypertensive agents. One-hundred consecutive hypertensive subjects with normal casual blood pressure after once-daily antihypertensive monotherapy treatment were studied. They were divided into three groups: group A, metoprolol (100 mg, daily); group B, atenolol (100 mg, daily); and group C, nadolol (80 mg, daily). Ambulatory blood pressure monitoring (ABPM) was used to evaluate the efficacy of the antihypertensive agents. The overall average ambulatory blood pressures were within the normal limits for all three groups. However, there were some abnormally high blood pressure (BP) readings shown on ABPM. Patients with an abnormally high systolic blood pressure (SBP) average > 140 mmHg accounted for 16.7% of group A, 19.4% of group B and 20% of group C. Those with an abnormally high diastolic blood pressure (DBP) average > 90 mmHg accounted for 16.7%, 19.4% and 10%, respectively, of the corresponding groups. There were no significant differences in the frequency of abnormally high SBP and DBP among the three groups. These "long-acting" antihypertensive drugs did not effectively control BP throughout the entire day. The duration of antihypertensive effect is not necessarily reflected by the blood half-life of the drug. ABPM is an effective way to ascertain the efficacy of "long-acting" hypertensive agents.