OBJECTIVE To compare an ultrafast CT method for estimating regional cerebral blood flow with a more commonly used xenon-enhanced CT method. METHODS Xenon CT and ultrafast CT were used to estimate regional cerebral blood flow (rCBF) in 12 healthy beagle dogs. Measurements were obtained for left and right hemisphere, cortical gray matter, basal ganglia, and deep white matter. The ability of each method to show differences in blood flow between regions of high flow (gray matter) and low flow (white matter) was evaluated, both for large (> 0.75 cm3) and small (< 0.5 cm3) regions of interest. In addition, side-to-side differences in rCBF were evaluated to determine the minimum difference that would suggest a significant alteration in blood flow. RESULTS There was less interanimal variance in absolute rCBF measurements obtained using xenon CT; ultrafast CT appeared to accentuate rCBF differences between high flow and low flow regions. There were strong side-to-side correlations in rCBF when measured by ultrafast CT, which suggests that this technique may be particularly useful in detecting focal alterations in rCBF restricted to one hemisphere of the brain. CONCLUSIONS Ultrafast CT measures of rCBF compare favorably with those obtained using xenon CT.