An improved method of canine auxiliary liver allotransplantation and effectiveness of antihistaminic drugs in preventing outflow block are described. The hepatic homograft is transplanted on the left side of the abdomen after splenectomy, which provides more room for the graft and vessels of sufficient size for vascular anastomosis of physiologic type. The results obtained in the second group of animals show that administration of antihistaminic drugs with the perfusate is effective in preventing outflow block syndrome.