Kinetic measurements were performed on marrow aspirates in 62 patients with various types of leukemia prior to chemotherapy. Higher labeling indexes were seen in chronic myelocytic leukemia and the blastic phase of chronic myelocytic leukemia than in the acute leukemias. In acute nonlymphocytic leukemia, kinetic measurements were correlated with clinical features and response to a chemotherapy program designed to synchronize cells to render them more susceptible to cycle-active agents or to a program given in a more conventional fashion. Age, sex, initial white blood cell and platelet counts, and presence of infection at time of diagnosis did not correlate with kinetic measurements or response to chemotherapy, but some clinical features did positively correlate with response to chemotherapy. Kinetic measurements correlated to some degree with response to therapy on one schedule but not on the other schedule.