The chemotactic peptide fMLP was known to induce adhesion, migration and phagocytosis of neutrophil. To clear the mechanism of the chemotaxis, the effects of PI3-K, p38 and ERK on actin polymerization were studied with the inhibitors of these kinases in neutrophil-like, differentiated HL-60 cells stimulated with fMLP. 0.1 μmol/L Wortmannin (PI3-kinase inhibitor) inhibited the fMLP-induced polymerization of actin. 50 μmol/L SB203580 (p38 inhibitor) and 50 μmol/L PD98059 (ERK inhibitor) did not inhibited it, though p38 and ERK were regulated by PI3-K. These results suggest the signaling pathway of actin polymerization mediated by PI3-K was different from that of p38 and ERK activation mediated by PI3-K.