The proliferation of bone marrow stem cell compartment is thought to be under both positive and negative controls by cytokines and colony stimulation factors. Macrophage inflammatory $protein-1{alpha}(MIP-1{alpha})$ has been assessed for its potential to protect hematopoietic stem cells from cytotoxic effects of a cycle-specific antineoplastic agents. We have tested the ability of $MIP-1{alpha}$ to suppress the proliferation of stem cell line Du.528.101 in variety of active status by using $[^{3}H]-thymidine$ incorporation test. The results were as follows. 1. The effect of $MIP-1{alpha}$ on steady-state Du.528.101 cell represented the cell growth suppression at the concentration of 10, 50, 100nM of $MIP-1{alpha}$(P<0.001). 2. $MIP-1{alpha}$ stimulated the proliferation of Du.528.101 cells previously treated with IL-1 at the concentration of 5, 50nM of $MIP-1{alpha}$(P<0.01). 3. The suppression effect of MIP-1 on Du.528.101 cells at the concentration of 5, 50nM was shown when cells were treated with $MIP-1{alpha}$ before activation with $IL-1{eta}(P<0.01)$. 4. The growth rate of synchronized cells were slower than that of non-synchronized ones, and $MIP-1{alpha}$ represented the similar suppression effect on both synchronized and non-synchronized cells.