AbstractSelected tests of lymphoid function were used to screen a population of volunteer hemapheresis donors. Testing included: 1) absolute lymphocyte numbers, and percentage of T‐cell, B‐cell, and mononuclear phagocytes, 2) serum immunoglobulins, and, 3) in vitro proliferative responses to lectin mitogens (phytohemagglutinin, concana‐valin A, and pokeweed mitogen), soluble antigens (staphylococcal filtrate, Candida, and streptococcal varidasc), and cell‐bound alloantigens (mixed lymphocyte culture). A control population of first‐time plateletpheresis donors was examined similarly. Regular donors manifested a small but statistically significant decrease in absolute lymphocyte counts (p<0.02), and IgM (p<0.02) compared to controls. Leukapheresis donors also manifested significant decreases in percentage of T cells (p<0.02). These findings are qualitatively similar to changes reported following intensive lymphocytapheresis and indicate the need for conservative policies regarding donation frequency in hemapheresis