We present two patients with chronic myeloid leukemia and hyperleukocytosis above 350 x 10(9)/l causing the symptoms of pulmonary leukostasis. Therapeutic leukapheresis procedures with concomitant chemotherapy were initiated within 12 hours from the diagnosis. After the therapy commencement the general condition of the patients systematically improved and leukocytosis gradually decreased from the second day of treatment with disappearance of pulmonary leukostasis symptoms. Thanks to application of such treatment procedures during the cytoreductive period, severe complications related to leukostasis could be prevented.