Phenotypic analysis of the autocytolytic lymphocytes. Peripheral blood lymphocytes from 6 patients with autologous GVHD were depleted of cells expressing the α/β TCR (n = 3) and the CD4 or CD8 cell surface determinants (n = 3) by immunomagnetic bead separation chromatography. Control cells were treated with normal mouse serum before separation. The depleted cell populations were tested for their ability to lyse pretransplantation, PHA-stimulated lymphoblasts. The results are expressed as the percentage of lytic activity depleted and were standardized against the control treated cells (100% activity; 0% lytic activity depleted) that had lytic activity ranging from 17.5% to 43.7% (mean ± SE percentage of specific lysis, 25.2% ± 4.9%).