Macrophage inflammatory protein-1 alpha (MIP-1alpha) is a member of the chemokine superfamily and has been observed to inhibit the proliferation of transiently engrafting stem cells, namely the colony forming unit-agar (CFU-A) stem cells. This study was initiated to investigate how MIP-1alpha exerts its inhibitory effect on these cells at the genetic level and, to examine whether altering the growth factors required for CFU-A colony formation could interfere with the inhibitory activity of MIP-1alpha. The results presented in this thesis indicate that growth factor alteration has minimal effects on the inhibition of CFU-A colony formation. However, low levels of MIP-1alpha in the presence of high levels of SCF or M-CSF have been observed to stimulate colony formation. This stimulatory activity of MIP-1alpha has been previously observed on progenitor cells however, it has never been reported on stem cells. Furthermore, alternatively shaped CFU-A colonies have been observed in assays containing high levels of both GM-CSF and MIP-1alpha. These results indicate that although the growth factors in the context of this assay can not interfere with the inhibitory signal of MIP-1alpha they may however interact with the other MIP-la signalling pathways. Although in the CFU-A assay SCF and IL-11 could not interfere with the inhibition of CFU-A colonies by MIP-1alpha, it was observed that upon the ex-vivo expansion of bone marrow, with SCF and IL-11, that the inhibitory activity of MIP-1alpha was reduced. This effect was observed to be specific for MIP-1alpha, as TGF-beta inhibition of CFU-A colony formation was not affected, and was proposed to be due to the down regulation of the MIP-1alpha inhibitory receptor. Indeed analysis of MIP-1alpha receptor expression indicated that CCR-1 was up-regulated whereas CCR3 and D6 were both down regulated, however neither CCR-3 nor D6 proved to be involved in MIP-1alpha inhibition of CFU-A colony formation. Therefore this study observed that in the context of the CFU-A assay that MIP-1alpha inhibitory signalling pathway is robust and minimally interacts with SCF, M-CSF, GM-CSF, IL-11 and LIF signalling pathways.