A cat stroke model was used to evaluate the efficacy of Dextran-40 (DEX) or Fluosol-DA 20% (FDA) in the treatment of focal cerebral ischemia. The animals were assigned randomly to one of three treatment groups: control, isovolemic hemodilution with DEX or isovolemic hemodilution with FDA. The oxidation state of cytochrome aa3 was measured in-vivo using near infrared reflectance spectrophotometry. The cerebral edema was measured by magnetic resonance imaging (MRI). The MRI edema indices for the three groups revealed that the FDA group had less edema (p less than 0.05), approaching that of non-stroke controls. The relative oxidation state of aa3 for the DEX group declined both during and after hemodilution. At the ninth hour post stroke the FDA group was better (aa3 more oxidized. p less than 0.025). Changes in blood and plasma components were reflective of the extent of hemodilution. Whole blood viscosity analysis revealed a difference (p less than 0.05) at the lower shear rates comparing DEX to FDA with FDA being higher than DEX. Two animals in each of the groups were allowed to awaken at the end of the procedure for functional assessment. These observations suggest that hemodilution with FDA following stroke significantly reduces early post-ischemic cerebral edema, improves oxidation in the peri-infarct area and appears to minimize functional deficits.