Endogenously produced and exogenously administered granulocyte colony-stimulating factor (G-CSF) has correlated with myeloid engraftment in a number of hematopoietic progenitor cell transplantation settings. Given the increased susceptibility of T cell-depleted (TCD) bone marrow transplants (BMT) to graft failure, a cohort of 36 (21 male and 15 female) recipients of TCD BMT was evaluated prospectively during the first month post-transplant for circulating serum G-CSF levels, to examine the correlation between myeloid engraftment and G-CSF levels. All recipients of TCD BM had measurable G-CSF levels, with a median peak level of 1750 pg/ml (range 540-26,250 pg/ml) occurring at a median of 5 days (range 1-18 days) after BM infusion. There was no association between G-CSF kinetics within 1 month post-transplant and the development of primary non-engraftment or secondary graft failure. One patient with primary non-engraftment and 6 patients with secondary graft failure exhibited median G-CSF peak levels of 1600 pg/ml and 1850 pg/ml (range 600-16,250 pg/ml) occurring 5 and 5.5 days (range 4-7 days) after BM infusion, respectively. Additionally, the patient with primary non-engraftment demonstrated a high G-CSF level in response to a low absolute neutrophil count (ANC). An inverse relationship between serial G-CSF levels and concomitant ANC was documented (log G-CSF = 6.19-0.009 ANC, P < 0.001). Higher peak G-CSF levels were associated with older recipient age (P = 0.01) and lower BM cell dose (P = 0.02), while administration of anti-thymocyte globulin post-transplant did not alter G-CSF levels.