Autotransplantation of splenic fragments has already been carried out in humans. The optimal size of the particles and amount of tissue required for this procedure has yet to be found. In normal young pigs and miniature piglets, autologous splenic tissue was transplanted into the greater omentum. The regenerated splenic mass, splenic blood flow, and histology were studied six months later. Implanting small splenic particles produced comparable results to implanting thin slices of splenic tissue. The mass of regenerated splenic tissue was only 3.1 g after implanting the whole spleen and 4.5 g after transplanting half of the spleen, which means 5.3% and 7.8% respectively of the weight of control spleens. The blood flow per gram in the regenerated splenic tissue was much lower than in the normal spleen. The blood flow in the whole of the splenic tissue is important for the clearance function of the spleen. Six months after transplanting the whole or half of the spleen, the blood flow to the regenerated splenic tissue was only 1% of that in the control minipigs. When half of the spleen was left in situ, as a model for a partial splenectomy, and the other half transplanted, the regenerated mass was only 3.4% of all splenic tissue and the blood flow 1.5% of the total splenic blood flow. In this model the regenerated splenic mass was independent of the size of the implants and the mass of implanted tissue. The extremely low blood flow indicates an inadequate clearance function and thus the protective function would probably be negligible.