Partially inbred miniature swine have been developed in this laboratory as a large animal model for immunologic studies. For many of these studies, a source of large quantities of well standardized antibodies to lymphocyte cell surface markers would be extremely helpful. Screening of a large panel of murine anti-human monoclonal antibodies (MAb) for anti-pig cross-reactions was nonproductive. We have therefore prepared a panel of MAb from mice immunized with pig thymocytes. Twenty-six stable MAb were produced that reacted with Ficoll/Hypaque-purified porcine lymphocytes. Reactivity was detected by complement-mediated cytotoxicity and/or cell surface binding ELISA. FMF analysis was performed on unseparated, glass-adherent, nylon wool-adherent, or nylon wool-nonadherent PBL and on cell preparations from lymphoid organs. In addition, the m.w. of the antigens detected by certain of these MAb were determined by immunoprecipitation of extracts of 125I surface-labeled cells. The majority of the MAb were not subpopulation specific. Included in these were 74-11-10 (IgG2b), which was specific for a polymorphic class I MHC determinant, and 76-3-2 (IgG1), which reacted with either a monomorphic class I MHC determinant or beta 2-microglobulin. Another MAb, 74-9-3 (IgM), precipitated a high m.w. complex of three polypeptide chains that appeared similar to that of the common leukocyte antigen. Of special interest were six MAb that were specific for various subpopulations of PBL: 76-7-4 (IgG2a) reacts with peripheral B cells, and 60% of thymocytes but not peripheral T cells, a pattern consistent with the murine ThB antigen; 74-22-15 (IgG1) and 76-5-28 (IgM) react with macrophages and granulocytes; 76-6-7 (IgM) reacts with T cells, macrophages, and granulocytes but not B cells, a combination of reactivities not previously reported in other species; 74-12-4 (IgG2b) and 76-2-11 (IgG2a) react specifically with T cells. 74-12-4 precipitated an antigen of 55,000 m.w., and 76-2-11 precipitated an antigen of 35,000 m.w. The m.w. and tissue distributions suggest that 74-12-4 recognizes porcine T helper cells, whereas 76-2-11 recognizes cytotoxic and/or suppressor T cells.