Because an airway-like inflammation has been reported in the gut of asthmatic patients, we sought to examine the expression of immunoregulatory cytokines like IL-4, IL-10, and IL-13 by gut mucosa. To establish this, we initiated this study to examine mRNA expressions of IL-4, IL-10, and IL-13 in duodenal mucosa from patients with asthma. Duodenal biopsy specimens were obtained from 20 asthmatic patients (10 allergic, 10 nonallergic) and 8 healthy controls. Cytokine mRNA was quantified with reverse transcriptase -Competitive PCR, and results were expressed in proportion to the number of β-actin mRNA in the same sample. IL-10 and IL-4 mRNA were detectable in all patients, whereas no IL-13 mRNA was detected. IL-10 mRNA concentrations were significantly higher in allergic subjects with asthma than in control subjects and nonallergic subjects with asthma. No significant difference was observed for IL-4. IL-10 mRNA expression was not related to asthma severity, FEV1, blood eosinophilia, or IgE levels. Our results support the hypothesis that IL-10 overexpression may counterbalance the effects of proinflammatory cytokines and mitigate the inflammatory reaction found in gut mucosa of subjects with asthma.