Objectives. This study aimed to demonstrate that irbesartan is successful in reducing diastolic blood pressure (BP) even following a missed dose after 6-8-weeks' treatment as measured by 24-hour ambulatory BP monitoring (ABPM). Methods. Eighty-eight patients (64 females, mean age: 53.4 +/- 10.6 years) with primary hypertension were included in this national, single-center, single-arm, open-label, prospective clinical study. Irbesartan (150 or 300 mg/day) was administered for 8 weeks. All patients were asked to cease treatment for l day during weeks 6-8. Changes in diastolic and mean 24-hour BP on the day of cessation and diastolic BP values during visits were efficacy parameters. Adverse events were also recorded.Resuhs. Systolic, diastolic, and mean BP values measured via ABPM before and on the day of a missed dose did not differ significantly. Irbesartan effectively controlled BP of the patients. BP normalization rates were 54% For 150 mg/day irbesartan only and 77% for both doses (150 or 300 mg/day) of irbesartan. None of the patients experienced serious adverse events throughout the study period. Conclusions. Irbesartan is successful and safe in the control of BP levels even following a missed dose at the end of a 6-8-week treatment period.