We prospectively evaluated the antihypertensive effect and tolerability of three different antihypertensive agents, losartan (angiotensin II receptor blocker), amlodipine (calcium channel blocker), and lisinopril (angiotensin-coverting enzyme inhibitor), in patients with mild-to-moderate hypertension. After a 2-week washout period, 121 patients were randomly allocated to three different groups for 12 weeks. Medications were titrated upward as necessary to achieve the goal office-recorded sitting diastolic blood pressure (SiDBP) (defined as SiDBP <90 mmHg or SiDBP > or = 900 mmHg but with a > or = 10 mmHg drop from baseline). Efficacy and tolerability were assessed after 4, 8, and 12 weeks of therapy with each regimen. At 12 weeks, significant differences in SiDBP compared with data of baseline were noted in all three groups ( P < 0.001 in all comparisons). Similarly, significant differences in the sitting systolic blood pressure compared with baseline data were also seen for all three groups ( P < 0.001 in all comparisons). The number of patients reaching goal SiDBP were comparable for the three groups: 25 patients (62.5%) in the losartan group, 27 patients (67.5%) in the amlodipine group, and 22 patients (59.5%) in the lisinopril group (not significant). Amlodipine produced a more pronounced reduction in SiDBP than the other two medications, although without statistical significance. Patients receiving lisinopril showed a high incidence of coughing (31.7%). Low leg edema was noted only in the amlodipine group (7.5%). Compared with the amlodipine and lisinopril groups, the losartan group seemed to have relatively fewer episodes (7.5%), and fewer patients (three cases) experienced adverse effects. In conclusion, this study demonstrates that losartan has the same antihypertensive effect, but has superior tolerability compared with the other two drugs. Coughing was a common side effect of lisinopril therapy in our population.