OBJECTIVE To study the possibility of using cellulose porous beads (CPBs) as a solid embolic material for the permanent occlusion of blood vessels. METHODS Unilateral renal arteries of 12 adult mongrel dogs were embolized with CPBs. Selective renal angiograms were obtained immediately, 1 hour, 4 weeks, and 12 weeks after the embolization. The dogs were killed 1 hour (n = 4), 4 weeks (n = 4), or 12 weeks (n = 4) after the procedure. The kidneys were removed en bloc and examined histologically. RESULTS The CPBs were easily injected through a microcatheter, were readily controlled with radiodensity, and did not adhere to the catheter. Renal angiograms obtained after embolization disclosed complete occlusion of the renal artery. Microscopically, the CPBs traveled to vessels with approximately the same diameter size. Larger vessels were occluded by aggregations of particles that left no open spaces. We found no disruption of the vessel wall, no evidence of perivascular hemorrhage, and no inflammatory changes of the vessel wall or the surrounding tissues. CONCLUSIONS The CPBs were easy to use; they reached distal sites and produced a homogeneous and permanent occlusion without specific inflammatory changes. The good results of this experimental study led to a clinical trial of CPBs.