In this prospective study, 24 patients with smoldering acute granulocytic leukemia received no specific treatment. Median survival duration from diagnosis was 9.29 months. Fourteen patients died of infection, four died of hemorrhage, two (8%) progressed to aggressive acute leukemia, and three remain alive at 36, 32, and 10 months. No survival predictions could be made from the severity of leukopenia, thrombocytopenia, or both. Neither sepsis nor hemorrhage, as causes of death, segregated into short- or long-term survivors (9.0 and 8.75 months' median survival, respectively). Thirteen patients (59%) had French, American, and British M2 subclassification of acute granulocytic leukemia. The following marrow findings distinguished this entity from preleukemia and other dysplastic states: clustering of stem cells; percentage usually between 20% and 40%; and Auer rods. The use of aggressive chemotherapy v only supportive measures in this condition remains unsolved.