Human polymorphonuclear leukocytes(PMN) constitute a first 1ine of defense against all forms of injury and microbial challenge, which share a common cell lineage with macro- phage. Microbial component LPS activates macrophages to produce IL-1, MIP-la, -lj3, TNF- a and IL-6, etc. Those cytokines have autocrine function to the macrophages, and paracrine function to other cell such as PMN and affect them to produce some biological functions. Having a responsive homogeneous cell line, HL-60, offers us the possibility of studying extensively on the function of PMN, which were not possible previously with peripheral PMN, due to the short-lived nature and difficulty of getting a purified PMN. In the present study, I performed MIP-1 receptor binding assay using HL-60 cell and human peripheral PMN. Also, in vitro antimicrobial assay was performed using differentiated or undifferentiated HL-60 cell. Differentiation was induced by treatment with 500 M of N,0-dibutyryl adenosine 3'5' cyclic monophosphate(dbcAMP) (PMN-like cell), or 20ng/ml of 12-0-tetradecanoylphorbol-13-acetate(TPA) (macrophage/monocyte-like cell). Receptors for MIP-la were identified on dbcAMP-treated HL-60 as well as peripheral PMN. However, bound radioactive MIP-la on differentiated HL-60 was much higher than that of peripheral PMN, which suggest receptor number of differentiated HL-60 cell is higher than that of peripheral PMN. Although both of TPA and dbcAMP treatment significantly enhanced antimicrobial action of HL-60 cell, dbcAMP-treated cell(PMN-like HL-60) killed S.aureus more effectively in this experiment. TPA or dbcAMP treatment significantly enhanced antimicrobial action of undifferentiated HL-60 cell. MIP-ln further increased enhancing effect of TPA or dbcAMP. IL-la, however, increased only dbcAMP-induced enhancing effect of antimicrobial action of HL-60 cell. These results suggest that differentiated HL-60 cell could replace peripheral PMN in analysis of various biological functions of cytokines on PMN cell.