BACKGROUND AND OBJECTIVES: Telmisartan (Micardis ), a selective type I angiotensin II receptor blocker, has recently been introduced as a new antihypertensive agent. We evaluated its anti-hypertensive effect and safety in mild to moderate hypertensive patients. MATERIALS AND METHODS: Telmisartan, 40 mg, was started once a day over the 4 week period in 45 patients with mild to moderate hypertension (35 male, mean age : 54.9 +/- 8.7 years). The dose was maintained in the patients whose blood pressures were controlled below 140/90 mmHg for the following 4 weeks. In those patients whose blood pressures did not fell below 140/90 mmHg, the dose was doubled to 80 mg per day for the following 4 weeks. Blood pressures were assessed at the 8th week of administration. For safety evaluation, laboratory tests were performed before and after treatment with telmisartan. Changes in heart rate and electrocardiogram were also observed. RESULTS: 1) The mean blood pressures in the sitting position were 161.6 +/- 14.7 mmHg(systolic) and 102.4 +/- 4.3 mmHg (diastolic) before treatment, which were lowered to 139.5 +/- 15.8 mmHg and 90.2 +/- 8.0 mmHg repectively after 8 weeks of treatment(p<0.05). 2) Heart rate was not significantly changed after treatment with telmisartan compared to pre-treatment (72.5 +/- 7.2/min vs. 71.7 +/- 7.5/min; p>0.05). 3) Laboratory tests revealed no significant abnormality by the treatment with telmisartan. 4) No significant side effects were observed during the treatment period. CONCLUSION: Telmisartan, 40 mg or 80 mg, once a day induced significant reduction in systolic and diastolic blood pressures without significant side effects in the patients with mild to moderate hypertension. Telmisartan is thought to be a well tolerated and effective antihypertensive medicine.