- Bromodeoxyuridine (BrdU) was administered to 128 newly diagnosed patients with standard risk acute myelocytic leukaemia (AML) for cell cycle measurements. Labelling indices (LI) were obtained from both the bone marrow aspirate (BMasp) and biopsies (bx) and durations of S-phase (Ts) and total cell cycle time (Tc) were measured by double-labelling the S-phase cells in vitro with tritiated thymidine. Median LI BMasp was 8% and from BMbx was 25%. The median Ts was 12 h (range 3.1-35 h) and Tc was 48 h (range 11.5-211 h). All patients received induction therapy with a combination of cytosine arabinoside and an anthracycline. Outcome of therapy or FAB type were not related to cell cycle characteristics. Patients with above median LI BMasp, however, had longer remission durations (P = 0.03) as did patients with above median Ts (P = 0.03) and Tc (P = 0.03). Upon longer follow-ups, even some of the patients with slowly cycling myeloblasts have relapsed (log rank P = 0.453 and 0.203 for Ts and Tc respectively). We conclude that patients with rapidly cycling cells tend to relapse faster; however, slowly cycling nature of myeloblasts is not associated with curability.