The kinetics of cytokine expression was evaluated in whole blood from high-IgE beagles previously sensitized to house dust mites (HDM) and known to develop clinical signs compatible with atopic dermatitis (AD) upon allergen exposure. Six high-IgE beagles were environmentally challenged daily for 3 h on three consecutive days with a HDM solution. Clinical signs were evaluated before, during, and after the conclusion of the challenge (days 0, 2, 4 and 17) and expression analyses of Th2 (IL-4 and IL-13) and regulatory (IL-10 and TGF-beta) cytokine mRNA were undertaken on blood samples at each time point using real-time polymerase chain reaction. Multiple comparison used to detect significant differences in clinical scores and expression levels of cytokine mRNA revealed that the clinical scores on days 2 and 4 were higher than those on days 0 and 17 (P < 0.05) but no temporal differences in the expression levels of IL-4 and IL-13 mRNA. Expression of TGF-beta mRNA was, however, significantly lower on day 4 (P < 0.05) and the expression of IL-10 mRNA on days 4 and 17 was significantly lower than those on days 0 and 2 (P < 0.05). The results indicate that allergen challenge decreases mRNA expression of regulatory cytokines in whole blood without enhanced mRNA expression of Th2 cytokines and suggest aberrant regulatory T-cell function in the immunopathogenesis of AD in high-IgE beagles.