The aim of the study was to assess the evolution of Alerting reaction (AR) under beta blocker treatment and to discuss its incidence on the management of arterial hypertension (AH). In 28 patients (pts), 19 men, 9 females, 46 +/- 12 years old, suffering from a mild to moderate AH, blood pressure (BP) was measured, according to a ritual circuit by a nurse (N), then a 12-minutes recorded monitoring, then a physician (Ph) using a mercury sphygmomanometer in upright, then in supine position at the end of the visit (165 +/- 18/108 +/- 13 mmHg, 161 +/- 14/100 +/- 9 mmHg). Pts received a cardioselective beta blocker, bisoprolol (B), 10 mg once daily and BP was evaluated after 1 and 2 months (D30; D60) under identical conditions. When compared to monitoring BP, there was a significant increase in systolic (S) and diastolic (D) BP, taken by the nurse and the physician, attributed to AR (delta SBP; delta DBP). Under B, AR remained unchanged, even increased regarding upright DBP at D30, D60 in spite of its efficacy: (formula; see text) The study demonstrates that there is no incidence of beta blocker on alerting reaction and that AR must be considered to evaluate the treatment and avoid an unnecessary or overtreatment. In case of discrepancies, it is suggested to perform an ambulatory BP monitoring.