PURPOSE: We examined age-related changes in baseline regional cerebral blood volume (rCBV) and response to acetazolamide stimulation by using dynamic contrast-enhanced MR imaging. METHODS: Thirty healthy volunteers ranging widely in age (23 to 82 years) were examined before and after intravenous injection of acetazolamide with dynamic susceptibility contrast-enhanced MR imaging. rCBV values were normalized for intersubject and intrasubject comparison by estimating an arterial input function directly from the imaging data. Preacetazolamide baseline rCBV and the percentage volume change index (PVCI) of the postacetazolamide to preacetazolamide state were calculated and examined as a function of age. RESULTS: Older adults (>50 years) had lower baseline rCBV per unit tissue than did younger adults (<50 years), but higher rCBV after acetazolamide stimulation. Baseline rCBV tended to decrease with age in the medial frontal and frontoparietal gray matter regions. Response to acetazolamide stimulation, measured by PVCI, showed a significant age-related increase in gray matter, approximately 0.5% per year. CONCLUSION: rCBV can be significantly increased after acetazolamide stimulation in the healthy aged. These results support the notion that age-related decreases in rCBV measured at rest reflect reduced regional metabolic requirements rather than reduced capacity for regional substrate delivery. These data serve as a normative baseline for comparison studies of rCBV vascular reserve in aging persons with various cerebrovascular disorders.