Under the assumption that in some patients with refractory anemia with excess of blasts (RAEB), the abnormal clones might be less responsive to granulocyte colony-stimulating factor than normal clones, the authors tried alternation therapy with a recombinant form of this factor (rhG-CSF) and antileukemic agents in the treatment of two patients with RAEB in transformation. After repetition of the short-cycled alternation therapy, the hematologic findings of both patients were completely normalized and have remained so without any adverse side effects under the continuation of this therapy for more than 5 months. Judging from our clinical experience, the alternation therapy may be a new efficient therapeutic strategy for RAEB and some types of slowly progressive leukemia.