G-CSF and GM-CSF both hasten myeloid engraftment post-MA-alloSCT; however, GM-CSF is earlier acting and less expensive. The objective was to evaluate efficacy/safety of sequential administration of GM-CSF followed by G-CSF in children post-MA-alloSCT. From January 2001 to June 2005, 31 children received 32 MA-alloSCT: mean age 6.65 yr; MRD BM or PBSC vs. related or unrelated UCB 11:21; malignant vs. non-malignant disorders 22:10. GM-CSF (250 microg/m(2) IV QD) began on day of stem cell infusion. GM-CSF was switched to G-CSF (10 microg/kg IV QD) when WBC >or= 300/mm(3) x 2 days. G-CSF continued until ANC >or= 2500/mm(3) x 2 days, then tapered to maintain ANC >or= 1000/mm(3). Median time to myeloid engraftment (ANC >or= 500/mm(3) x 3 days) was 17 days [13 days vs. 24 days, MRD BM/PBSC vs. UCB (p < 0.0001)], occurring at a median time of two days after switch to G-CSF. Clinically relevant adverse events were bone pain (n = 8) and large pleural effusion (n = 1). It was estimated that sequential GM-CSF/G-CSF was cost-effective compared with G-CSF alone [cost-savings of $1311/patient ($41,952/study), 2007 Red Book Average Wholesale Price]. In summary, it was demonstrated that sequential administration of GM-CSF/G-CSF post-MA-alloSCT was safe, cost-effective and resulted in prompt myeloid engraftment.