Chemotherapy (CT) induced critical neutropenia remains a major dose limiting problem in acute leukemias. In order to reduce the phase of risk we gave recombinant human GM-CSF to 30 patients at high risk of early death with acute myeloid leukemia (AML). 19 patients with untreated AML and 1 patient with AML late relapse were 65+ years of age and were treated for CT by the TAD9 regimen. 10 patients at all ages had AML early or second relapse and received S-HAM CT. Starting on day 4 after CT GM-CSF 250 micrograms/m2/d was given by continuous i.v. infusion until neutrophils recovered. GM-CSF reduced the median recovery time of neutrophils by 4 days in the TAD9 and 9 days in the S-HAM CT group when compared to controls. After the CT induced aplasia 3 patients with AML showed a regrowth of their blasts which after the stop of GM-CSF was reversible in 1 patient and unaffectedly continued in 2 patients. 57% of patients attained a complete remission, and the median age of the responders was 65 (34-84) years. Remission duration was not found to be reduced. Thus, GM-CSF reduces CT toxicity with a low risk of promoting the disease and may allow more effective antileukemic treatment.