Abstract: 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 μg/m2 IV QD) began on day of stem cell infusion. GM-CSF was switched to G-CSF (10 μg/kg IV QD) when WBC ≥ 300/mm3 × 2 days. G-CSF continued until ANC ≥ 2500/mm3 × 2 days, then tapered to maintain ANC ≥ 1000/mm3. Median time to myeloid engraftment (ANC ≥ 500/mm3 × 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.