A patient with Sezary syndrome underwent cytapheresis on the IBM 2997 cell separator. Four procedures were performed over a 12-day period. A total of 8.3 x 10(10) Sezary cells were removed. The patient's skin lesions and lymphadenopathy regressed. Transient thrombocytopenia occurred, requiring platelet transfusion. Although a significant number of platelets were removed by pheresis, this was not sufficient to explain the thrombocytopenia. The patient subsequently died of causes unrelated to the cytapheresis.