The purpose of this study was to determine if immunotherapy with Krestin can prolong the durations of complete remission and survival. The patients were placed at random in the chemotherapy and chemoimmunotherapy groups. The median durations of complete remission and survival were longer in the chemoimmunotherapy group than in the chemotherapy group. The complete remission rate of the second induction was higher in the chemoimmunotherapy group than in the chemotherapy group. The cell-mediated immunity was somewhat enhanced in the chemoimmunotherapy group, while it was not enhanced in the chemotherapy group. These results suggested that Krestin administration for maintenance therapy was useful for prolongation of the durations of remission and survival time in patients with acute leukemia.