It is frequently useful in studies of transplantation to have available an antibody to a cell surface antigen, which is not itself responsible for transplant rejection. In this paper, we identify and describe such an antibody/antigen system in miniature swine. The monoclonal antibody, 1038H‐10‐9, was found to react to a pig allelic antigen (called PAA), found on a variety of pig cells and tissues, including peripheral blood mononuclear cells (PBMC), thymocytes, lymph node, bone marrow, and skin. Analysis for recipient sensitization against PAA was performed by in vitro cell‐mediated lympholysis (CML) assay, mixed lymphocyte reaction (MLR) assay, antibody binding studies, and skin graft rejection patterns were examined. No evidence was found to indicate detection of PAA by any of these assays of alloreactivity. We therefore conclude that PAA is an allelic swine cell surface antigen, with wide tissue distribution, and that it is not a histocompatibility antigen. It should provide a powerful tool for studies of transplantation biology in miniature swine, such as identification and quantification of chimerism following organ transplantation.