Macrophage inflammatory protein-la(MIP-la) from activated T cell or macrophage, which is small inducible cytokine of unkown biological function, has been shown to display inflammation chemokinetic activities, as well as myelosuppressive effect on more immature progenitor cells. In this paper we show the MIP-1a mRNA expression and the presence of MIP-la binding sites from murine macrophage cell line RAW 264. 7 and primary cells of mouse bone marrow and spleen. MIP-la mRNA was induced from LPS-stimulated RAW 264. 7, but not inhibited by cyclosporin A treatment, and also was expressed from mouse splenocyted and bone marrow cell which were not increased by ferritin or lactoferrin treatment. The results of receptor binding assay showed that radiolabeled RAW 264. 7 cell with kd value of 0.91 nM, and binding sites per cell of 378. Bone marrow cell and splenocyte also appeared to have MIP-1a binding sites 33 and 11 per cell, respectiviely.