To investigate the effects of specific immunotherapy on the NKT cells in peripheral blood and the ability of NKT cells to proliferate in response to alpha-galactosylceramide (alpha-GalCer) in house-dust-mite- (HDM-) sensitized asthma children, peripheral blood mononuclear cells were isolated from 42 asthmatic children, of whom 24 were on specific immunotherapy (SIT) for more than a year and 20 were healthy. Compared with control group, the ratio of peripheral blood NKT and CD4(+)NKT cells was significantly decreased (P < 0.01) and was elevated in SIT asthma group (P < 0.05), respectively, but it was still less than the normal control group (P < 0.01). The level of IL-4 in serum secreted by NKT cells in asthma group was significantly higher than that of control group (P < 0.01), particularly apparent after 72 hours. The level of IL-4 in SIT group decreased significantly (P < 0.01). The level of IL-10 in serum secreted by NKT cells in asthma group was decreased significantly than that of the control group (P < 0.01) especially in 48 hours, while that of SIT group was increased significantly (P < 0.01). These results suggest that the pathogenesis of asthma may be related to the ratio and dysfunction of NKT and CD4(+)NKT cells.