AIM: To investigate the amount and patterns of expressing CD69 , IL-4 and IFN-? on TCRV?24 +NKT cells, and compare with that of CD3 +T cells from human peripheral blood in response to in vitro stimulation. METHODS: The whole blood was stained with three-color immunofluorescence directly or after cultured with PDB+ionomycin(Ion) for 6 h, then the mononuclear cells were separated by lysing red blood cells. The expression rates of CD69, IL-4 and IFN-? on TCRV?24 +NKT cells and CD3 +T cells were estimated by flow cytometer. RESULTS: As a proportion of mature T cells, the ratio of TCRV?24 + NKT cells to CD3 +T cells was about(1.34?0.42)%. The expression rates of CD69 on TCRV?24 + NKT cells and CD3 +T cells in response to PDB + Ion for 6 h were (96.71?1.33)% and (98.60?0.47)%, respectively, while the ratio were (11.47?2.86)% and (1.07?0.45)% in the unstimulated group, and there were significant difference between them. The expression rates of IL-4 and IFN-? on TCRV?24 +NKT cells stimulated with PDB+Ion for 6 h were (48.62?2.44)% and (46.65?8.91)%, respectively ,which were significantly higher than that of unstimulated group [(31.57?3.31)%, (13.45?6.29)%] and that of stimulated CD3 +T cells, though the expression rates on stimulated CD3 +T cells were significantly higher than that of unstimulated CD3 +T cells. CONCLUSIONS: There is small amount of NKT cells in adult human peripheral blood. The expression rates of IFN-? and IL-4 on these lymphocytes are higher than CD3 +T cells, suggesting that NKT cells are important immunomodulatory cells in special microvironments.