We describe the case of a 12-year-old boy affected by cyclic neutropenia, at high risk of developing life-threatening infections, treated with recombinant human granulocyte-macrophage colony stimulating factor (rHuGM-CSF). The drug was effective in reducing the severity of neutropenia and infectious complications in our patient. It was administered for brief periods of time, in contrast to the daily continuous administration reported for rHuG-CSF. Therefore, more extensive studies must be performed to identify the most effective time schedule for the drug. In vitro studies of hemopoietic progenitor cells were useful, in this case, to predict treatment response.