In a randomized study of 18 adult patients with high-risk or advanced acute myeloid leukemia (AML) we investigated the effect of supplementing conventional induction chemotherapy with recombinant human granulocyte-macrophage colony-stimulating factor (rhGM-CSF). For comparison, a historical control group of 90 patients treated for de novo AML with conventional chemotherapy during the previous period, 1984-1990, was also analyzed. Before induction chemotherapy, 10 patients were randomized to receiving rhGM-CSF, starting on day 1 to 3 before chemotherapy and continued for a maximum of 21 days after the start of induction treatment. Fatal complications and treatment outcome did not differ between the study groups and historical controls. Nor were there any differences between the groups in terms of hematological toxicity, e.g. time to three-lineage regeneration and need for supportive therapy. However, sequential weekly bone marrow examinations revealed a prolonged reduction of the relative number of myeloid (CD33-positive) marrow cells in the rhGM-CSF treated group. Although the small number of patients studied may not permit a definite conclusion, this randomized study did not demonstrate major beneficial effects of combining rhGM-CSF with standard induction chemotherapy in high-risk patients with AML.