OBJECTIVE To study the molecular mechanism of tetramethylpyrazine to induce human promyelocytic HL-60 leukemia cells differentiation. METHODS The cell proliferation was determined by MTT. The differentiation of the cells was detected by NBT reduction test. Cellular morphology was observed by Wright's staining. Cell cycle distribution and the distribution of CD11b, CD14 were detected by flow cytometry. Then RT-PCR and Western blot assay were employed to detect the expressions of c-myc, p27, CDK2 and cyclinE1 in HL-60 cells after exposure to TMP. RESULTS TMP inhibited the proliferation in a dose and time dependent manner. TMP at the concentration of 200 mg x L(-1) to 300 mg x L(-1) induced unterminal differentiation of HL-60 cell and synergistically blocked the cell cycle progression of HL-60 cells in G0/G1 phase. The expression of c-myc was down-regulated as well as the protein expression of cyclin E and CDK2, while the mRNA and protein expression of P27 were remarkably up-regulated. CONCLUSIONS Small doses of TMP induces differentiation of HL-60 cells throughout the cell cyde, as detected by a slower rate of accumulation in G0/G1, possibly by regulating the expression and activity of G1/S phase-related molecules.