This study was initiated in order to assess any immunologic effects that source leukocyte concentrate collection might have on double-bag plasmapheresis donors. Previous studies have shown that surveillance parameters, such as T versus non-T lymphocyte subpopulations, showed no abnormal values in donors with as many as 500 visits over a 12-year period. The present study demonstrates that the frequency and the total number of leukocyte donations do not effect the lymphocyte subpopulations and functions observed. No significant changes were noted for specific and nonspecific stimulation, natural killer (NK) cell activity, lymphocyte surface markers and a variety of functional parameters. For example, the apheresis donors manifested no differences in NK cell activity, human leukocyte interferon production, IgG synthesis by B cells and percent suppression of both IgG synthesis and mixed lymphocyte cultures, when compared to non-apheresed donors.