Purpose: Seven children with newly diagnosed acquired severe aplastic anemia (SAA) were treated with a combination of longterm granulocyte-macrophage colony-stimulating factor (GMCSF) and immunosuppression to assess the potential for GMCSF to induce sustained neutrophil recovery, reduce the incidence of infection, and enhance the therapeutic efficacy of immuno-suppression. Methods: Patients received a 14-day course of i.v. antithymocyte globulin 15 mg/kg/day with oral prednisone 1 mg/kg/day, long-term daily oral cyclosporine A 10 mg/kg/day, and long-term daily s.c. GM-CSF 5 mu g/kg/day. Results: All seven children recovered an absolute neutrophil count of >1.0 X 10(9)/L within 3.5 months of diagnosis (mean 60 days). Of the six children followed throughout their entire illness (follow-up 10-27 months), five are platelet and red cell transfusion independent (three off-therapy, two on tapering therapy) and one continues on therapy with a diminishing transfusion requirement. Compared with seven children treated previously with immuno-suppression alone, children who received GM-CSF spent fewer days in the hospital and were less likely to develop infection. Conclusions: The addition of GM-CSF to immunosuppressive therapy appears to be beneficial in the treatment of children with acquired SAA with GM-CSF stimulating granulopoiesis. The children are better protected from infectious complications while immunosuppressive agents achieve full therapeutic potential.