Blood vessels and their endothelial lining are major stimulators and targets of the rejection response. The immunological properties of human endothelial cells differ significantly from those of other species and new models are needed for proper study of human vessels in the transplant setting. We have employed the human peripheral blood lymphocyte/severe combined immunodeficiency (huPBL/SCID) mouse for this purpose. We describe here our results involving transplantation of human skin, human artery and cultured human endothelial cells. We also describe our more limited experience using porcine skin and artery transplantation to study human T cells responses to pig endothelium.