Sequential studies in acute myeloid leukemia of bone marrow cells in agar culture showed striking fluctuations of colony and cluster formation during induction of remission. These oscillations may be initiated by recruitment of resting leukemic and normal cells upon chemotherapeutic perturbation. Striking oscillations of the colony and cluster formation occurred also during remission with or without maintenance therapy, but with a longer periodicity as compared to the phase of induction of remission. Oscillations of the marrow growth capacity during remission may reflect potential relapses where the outcome depends on proliferative advantages of the normal or leukemic cell clone.