Colony stimulating factors (CSFs) regulate production of myeloid cells. Use of CSFs post bone marrow transplant accelerates granulocyte recovery by shortening the interval of relative but not absolute granulocytopenia. Data from non-randomized trials suggest that CSFs decrease documented infections by about one-third; there is no apparent increase in survival. Adverse effects of CSFs are modest; there are no indications of increased graft failure, graft-versus-host disease or cancer recurrence after their use. Future studies of CSFs should be in the context of randomized trials where their therapeutic efficacy is best evaluated. CSFs may also be useful in other transplant settings such as treating graft failure or increasing the efficiency of harvesting myeloid progenitor cells from the blood for subsequent transplantation. Controlled trials are needed to evaluate these uses. Future directions will probably include combinations of CSFs and, possibly, in vitro treatment of the graft.