Purpose: To compare the in vivo distribution of the new embolic Embozene versus Embosphere as a control in the sheep renal and uterine vasculature. Materials and Methods: Twelve sheep (three per group of product and size) were selectively embolized with Embozene 700 mu m, Embozene 900 mu m, Embosphere 500-700 mu m, or Embosphere 700-900 mu m, in one renal artery (0.5 mL microspheres) and in the two uterine arteries (0.25 mL each) and sacrificed 72 hours later for pathologic examination of kidney and uterus. Partition of microspheres in the vasculature was determined according to a classification of the renal and the uterine vasculatures into several zones. Vascular diameters and microsphere deformation were measured. Results: Embozene 700 mu m and Embozene 900 mu m occluded significantly more distally than Embosphere 500-700 mu m and Embosphere 700-900 mu m in renal and uterine vasculature. For Embozene, the vessel diameter was not significantly different between the two sizes, for each organ, whereas it was significantly larger for Embosphere 700-900 mu m than for Embosphere 500-700 mu m in each organ. Embozene deformation was significantly higher than that of Embosphere in renal and uterine vasculature, increased from proximal to distal in location for both organs and correlated negatively with vessel diameter (Rho = -0.623; P < .0001). Embosphere deformation did not vary according to the zone. Conclusions: Embozene microspheres have a higher in vivo deformation, which results in a more distal occlusion within the vascular network compared with reference Embosphere microspheres. The diameter of occluded vessels varied for the tested size range for Embosphere but was independent of the tested microsphere size range used for Embozene. The deformation of Embozene appears to determine the size of the vessels occluded as opposed to the granulometric particle size, which makes level of occlusion unpredictable.