Platelet and granulocyte collections have been done for the past 15 years, and studies on the safety of these procedures have been carried out in many institutions in the USA and abroad. In general, no long-term harmful effects have been observed in donors who had undergone frequent cytapheresis. Significant decreases in donor platelet count were noted following repeated platelet apheresis. However, only a few donors became thrombocytopenic (platelet count less than 150,000/microliter). Interestingly enough, if the donor was allowed time to recover a normal platelet count, subsequent repeated platelet collection did not induce thrombocytopenia. Rebound of platelets has also been a common finding. Intensive granulocyte collections have not reduced the number of circulating granulocytes, nor has there been any report of leukopenia in donors who had undergone frequent leukocytapheresis. The limiting factor has been the need for hydroxyethyl starch as a sedimenting agent and corticosteroids to stimulate the granulocyte release from the marrow, which have known adverse effects of their own. No significant changes in plasma proteins and other biochemical and hematological parameters have been reported in cytapheresis donors. There is widely-held concern that because the collections of platelets and granulocytes are not selective to the exclusion of lymphocytes, the repeated cytapheresis may deplete the circulating lymphocytes with theoretical risk associated with long-term alterations of the immune response. In addition, if a significant number of red blood cells are removed, the frequent apheresis donations may render the donor anemic. Because of these theoretical risks, recommendations have been formulated in the USA in an attempt to ensure the safety of apheresis donors.