INTRODUCTION: Primary hypertension can be masked and be responsible of a severe impact on the target bodies. The purpose of this study was to see if Phenobarbital at low dose is able to decrease the sympathetic hyperactivity assessed by cardiovascular autonomic reflexes in patients with masked hypertension. MATERIALS AND METHODS: This prospective study was conducted on a total of 91 patients with masked hypertension average age 52.1 10.3 years old . ...