To determine whether any lymphocyte subset is preferentially harvested and transfused as a consequence of plateletapheresis with the Fenwal CS-3000 Blood Cell Separator, the proportions of lymphocyte subpopulations in platelet concentrates were compared to their proportions in the donors' peripheral venous blood immediately prior to platelet collection. There was no difference in the proportion of B cells (surface immunoglobulin positive), T cells (OKT3 positive), helper/inducer T cells (OKT4 positive), suppressor/cytotoxic T cells (OKT8 positive), and natural killer cells (Leu 7 positive) in the donors' peripheral venous blood and the plateletapheresis product. Thus, although previous studies have demonstrated the ability to separate lymphocyte subpopulations by density centrifugation and velocity sedimentation, plateletapheresis with the CS-3000 harvests the lymphocyte subpopulations studied in the same proportions in which they circulate in donors' peripheral venous blood.