Repetitive Transcranial Magnetic Stimulation (rTMS) has been recently employed as a therapeutic strategy for stroke, although its effects on cerebral hemodynamics has been poorly investigated. This study aims to examine the impact of high frequency rTMS on cerebral vasomotor reactivity (VMR).Twenty-nine healthy subjects were randomly assigned to real (19) or sham 17-Hz rTMS, applied on primary motor cortex (M1) of the dominant hemisphere. All subjects underwent Transcranial Doppler of the middle cerebral arteries to evaluate mean flow velocity and VMR before (T 0 ) and within 10min (T 1 ) following rTMS. Four subjects underwent further VMR evaluations at 2 (T 2 ), 5 (T 3 ) and 24h (T 4 ) after rTMS. As a control condition, 10 subjects underwent real (5) or sham rTMS on calcarine cortex. In addition, five acute stroke patients underwent five daily rTMS sessions on the affected hemisphere mimicking a therapeutic trial.Following real rTMS on M1 (p=0.002) and calcarine cortex (p<0.001) VMR decreased with respect to T 0 in both hemispheres, while no change was observed after sham rTMS (p>0.6). VMR tended to remain lower than T 0 until T 3. Cerebral VMR decreased independently of the stimulated side also in the patients’ group.High frequency rTMS reduces cerebral VMR, possibly as a secondary effect on autonomic control of cerebral hemodynamics.The effect of rTMS on cerebral hemodynamics should be carefully considered before proceeding toward a therapeutic application in stroke patients.