Abstract
In 31 children with acute leukemia, the proliferative activity of the leukemic marrow cell population as measured by mitotic and labeling indexes varied widely from patient to patient and from one disease stage to another. Leukemic marrow had a small but statistically significant diurnal variation of proliferative activity. Changes in labeling indexes were directly related to changes in the proportion of large dividing blasts in the marrow. Generation times of dividing leukemic blast cells in 3 patients were similar at diagnosis and in relapse. Changes in proliferative activity of leukemic marrow can be explained by progressive accumulation of nondividing leukemic cells.