The early stage of hemodynamic failure in ischemic cerebrovascular diseases is characterized by diminished cerebrovascular reserve. Tissues at this stage are at high risk for stroke. Assessment of cerebrovascular reserve by cerebrovascular reactivity (CVR) measurement usually requires the administration of vasoactive challenges (e.g., acetazolamide or CO2), which is often difficult or impractical in stroke patients. In this study, we demonstrate that CVR can be mapped in stroke patients without a physiological challenge but using the natural fluctuations of the resting-state BOLD signal. Results indicate that this technique can assess CVR in lesion, peri-lesional, and healthy tissue in a reproducible manner.