OBJECTIVES: To prospectively define the lowest possible doses of recombinant human granulocyte colony-stimulating factor (rhG-CSF) that would benefit selected children with chronic idiopathic neutropenia whose disease was severe enough to interfere appreciably with quality of life. STUDY DESIGN: The efficacy of low-dose rhG-CSF therapy was investigated in six children with symptomatic chronic idiopathic neutropenia. All patients received rhG-CSF, 5 μg/kg subcutaneously, as a single daily dose until an absolute neutrophil count (ANC) above 1.5 × 10⁹/L was observed. The rhG-CSF dosage interval and amount were then increased and decreased, respectively, in an alternating fashion until the lowest rhG-CSF dose that would maintain the ANC above 1.0 × 10⁹/L (1000/mm³) was reached. RESULTS: Although the minimal dose requirements varied, all patients were able to maintain a mean ANC >1.0 × 10⁹/L during a mean follow-up period of 14 months at doses ranging from 1.0 μg/kg once weekly to 5.0 μg/kg every other day. Administration of rhG-CSF resulted in resolution of all preexisting chronic infections, reduction in the frequency of new infectious episodes, and discontinuation of prophylactic antibiotics. In all patients the ANC decreased to pretreatment values when further reduction or discontinuation of rhG-CSF therapy was attempted. By identifying the minimal effective dose in each patient, we were able to reduce the treatment cost by a mean of 81% compared with daily dosage at 5 μg/kg. CONCLUSIONS: Recombinant human granulocyte colony-stimulating factor therapy at low doses (≤5 μg/kg) every 2 to 7 days to symptomatic children with chronic idiopathic neutropenia is effective and no more costly than supportive treatment with antibiotics. (J PEDIATR 1996;129:551-8)