Objectives: We sought to determine whether the aryl hydrocarbon receptor (AhR) and interleukin (IL)-22 may be involved in the pathogenesis of the peripheral blood mononuclear cells (PBMCs) in allergic asthmatic patients and whether their expression may be related to the severity of the disease. Methods: Blood samples were obtained from each subject with allergic asthma (n =18), controlled asthma (n =17) and healthy controls (n =12) respectively. The PBMCs were collected for AhR mRNA detection by real-time quantitative polymerase chain reaction (PCR). The plasma was collected for IL-22 protein detection by enzyme-linked immunosorbent assay (ELISA). Results: The expression of AhR mRNA in PBMCs and IL-22 protein in plasma of patients with allergic asthma were higher than those in controlled asthma cases and healthy controls. The plasma concentrations of IL-22 had negative correlation with the predicted percentage of forced expiratory volume in the first second (FEV(1)%) and the percentage of FEV(1) and forced vital capacity (FEV(1)/FVC%) and it was positively correlated with the asthma severity score (ASS) of the asthmatics. Conclusion: Our results suggested that both AhR and IL-22 might be involved in the pathogenesis of allergic asthma in human and the level of IL-22 might have some relationship with the severity of the disease. (Asian Pac J Allergy Immunol 2011;29:266-72)