Apoptosis (programmed cell death) is accompanied by loss of phospholipid asymmetry, i.e., translocation of aminophospholipids such as phosphatidylserine to the outer leaflet of the plasma membranes, which results in recognition of these cells by macrophages. In the present study, I studied on the involvement of beta 2-glycoprotein I (beta 2-GPI) and anti-beta 2-GPI antibodies in apoptotic lymphocytes. By flowcytometric analysis, I demonstrated that beta 2-GPI could bind to a human T cell line, Jurkat cells, treated with an anti-Fas antibody, CH11. beta 2-GPI-bound cells were detected 2 hr later after anti-Fas treatment and the most cells were bound to beta 2-GPI by 6 hr later. The accumulation of beta 2-GPI-bound cells paralleled with morphological changes and DNA fragmentation of the cells. I also demonstrated that anti-beta 2-GPI antibodies and a beta 2-GPI-dependent anti-cardiolipin antibody, established from a patient with antiphospholipid syndrome, could recognize beta 2-GPI-bound Jurkat cells treated with anti-Fas-antibody. These results imply that beta 2-GPI and anticardiolipin antibody may have a role in the clearance of apoptotic cells from the blood stream.