After hepatic artery embolization with Gelfoam powder in five rabbits, two colors of Microfil (silicone rubber solution) were perfused into the aorta and the portal vein to study hepatic microcirculation under a dissection microscope. In three of the animals, many intrahepatic arterial branches and portions of the hepatic sinusoids were perfused with the arterial Microfil (orange color), whereas in the other two animals no orange Microfil was found in the liver. In the three animals, occlusions of the hepatic artery were random in distribution and often segmental, and arteries as small as 50 microns in diameter were involved. In the latter group, levels of arterial occlusion could not be evaluated. Microcollaterals developed through the capsular artery, peribiliary arterial plexus, and vasa vasora of the portal vein.