Cyclic cytotoxic maintenance therapy can be applied to patients with AML in post-remission. We studied the immune status of AML patients in complete remission and the effect of maintenance therapy on different immune cell populations. Patients in complete remission had reduced NK, T H and T reg counts and a reduced NK activation capacity. In the course of cytotoxic maintenance therapy, NK counts further declined, while T H and T reg cells increased, with lower proliferative potential of T H cells. We conclude that immunotherapeutic approaches in post-remission have to consider reduced NK cell function and further impairment of cellular immune responses during cytotoxic therapy.