To evaluate the sensitivity of the intravoxel incoherent motion (IVIM) technique to changes in cerebral blood flow, we made measurements of IVIM parameters in rat brain under conditions of altered arterial pCO2. The arterial pCO2 was varied over a range which would be expected to change cerebral blood flow from roughly 50 to 500 ml/(100 g.min). The IVIM measurements were made with suppression of extravascular water signal. The parameters f' (the apparent fraction of spins which have "fast" pseudodiffusion), D1* (the "fast-pseudodiffusion") coefficient), and D2* (the "slow-pseudodiffusion" coefficient) all showed statistically significant positive linear correlations with arterial pCO2. These results suggest that the IVIM method, when used with suppression of extravascular water signal, is sensitive to changes in blood flow.