Fifty-four mAb preselected in the first round of the first porcine CD workshop for their possible reactivity with T-lymphocyte specific antigens and/or activation antigens were further analysed in a second round. PBMC, thymocytes and nylon-wool purified T lymphocytes derived from peripheral blood, mesenteric lymph nodes and spleen served as target cells for flow cytometric analyses. For the classification of activation antigens several experiments were performed with activated, mitogen-stimulated T lymphocytes and long-term T-lymphocyte cultures. Out of the 54 mAb, 35 mAb could be distributed to six different CD clusters and two swine workshop clusters (SWC). Five mAb could be distributed to the porcine CD2, four mAb to the CD4. Six mAb seemed to recognize the porcine CD5 and two mAb the porcine CD6 analogue. Six mAb were directed against the porcine CD8, whereas two different epitopes could be defined. One mAb was directed against the porcine CD25 analogue. Nine mAb could be clustered to the SWC1, defining an antigen on T lymphocytes and cells of the myeloic linage. Two mAb with high T-cell specificity were clustered to the SWC2.