A panel of cytotoxic monoclonal antibodies (Moab) derived from mice immunized with porcine thymocytes has been developed which reacts with monomorphic determinants on porcine peripheral blood lymphocytes (PBL). These Moab recognized from 25% to 100% of PBL as tested by flow microfluorimetry One of the Moab (PT 81) that bound 39% of PBL, 30% of splenocytes and 65% of thymocytes as determined by flow microfluorimetry was selected for initial characterization. PT 81 specifically lysed 37% of Ficoll/Hypaque-prepared PBL depleted of monocytes by carbonyl iron ingestion. This antibody lysed 47% of T cells (PBL that formed dextran-enhanced, sheep erythrocyte rosettes; P less than 0.001) and 64% of a T cell subset (PBL that formed dextran-enhanced, porcine erythrocyte rosettes; P less than 0.001) when compared to cells treated with complement alone. Lysis of PBL with PT 81 plus complement caused a 100% enrichment in the number of surface immunoglobulin positive cells (P less than 0.01). The conclusion that PT 81 does not recognize B cells was further supported by double labelling experiments. Removal of PT 81 positive cells did not significantly affect the number of cells with C3b (zymosan-complement rosettes) or Fc gamma (erythrocyte-antibody rosettes) receptors. PBL that were treated with PT 81 plus complement were passed over Ficoll/Hypaque (density 1.09) to remove dead cells. The PT 81-depleted lymphocyte population displayed only 20%, 20%, 26% and 29% of the proliferative responses of control cells treated with complement alone (P less than 0.01) to several concentrations of the mitogens phytohemagglutinin, concanavalin A, soybean agglutinin and pokeweed mitogen, respectively.(ABSTRACT TRUNCATED AT 250 WORDS)