Background: Atropine is an anticholinergic drug which is commonly used in clinical practice. The effect of parasympa-thetic block with atropine on dynamic cerebrovascular regulation remains unclear. This study was aimed to identify ef-fects of vagolytic atropine on cerebrovascular response during acute orthostatic hypotension in humans. Methods: Continuous middle cerebral blood flow velocity (CBFV, transcranial Doppler) and arterial blood pressure (ABP, Finometer) were measured during a sit-to-stand procedure in 10 healthy subjects with placebo and vagolytic (10 μg/kg) doses of atropine. Cerebral vascular tone was assessed by cerebrovascular resistance (CVR = ABP / CBFV). Dynamic ce-rebral autoregulation was also assessed by transfer function analysis of ABP and CBFV. Results: During the standing session, ABP fell to a similar extent in both groups by an average of 23 to 25 mmHg (26% to 29%). CBFV also fell in all subjects but significantly more in vagolytic atropine (-15.0 ± 7.0 cm/s) compared with pla-cebo (-12.0 ± 5.8 cm/s, P < 0.05). CVR was decreased significantly in the placebo group during posture change (1.56 ± 0.44 vs. 1.38 ± 0.38, P < 0.05), in contrast, lesser decreased in the atropine group (1.60 ± 0.50 vs. 1.53 ± 0.42, P = 0.193). Transfer function coherence in the very-low-frequency range was significantly increased in the atropine group during the standing session (0.55 ± 0.14), compared with the sitting session (0.45 ± 0.14, P = 0.006). Conclusions: These data present that vagolytic atropine attenuates cerebral vasodilation response to acute orthostatic hy-potension, suggesting the use of atropine may need care in patients with cerebrovascular disease with vagal impairment.