We used in vitro model of storage-induced leukocyte degradation in blood to experimentally characterize the infectivity of the debris of lymphocytes harboring human immunodeficiency virus (HIV-1). The leukocyte filtration process removed both intact HIV-infected H9 cells and the particulate debris, but failed to remove the cell-free HIV released from lysed cells. These data suggest that the leukocyte filtration of donor blood soon after collection would optimally reduce the particulate infectious burden of blood for transfusions.