Levels of pro-allergic cytokine IL-4 are increased in asthmatic airways, contributing to allergic inflammation. IL-4 and IL-13 are the most important factors in production of class E immunoglobulin, playing major role in childhood atopic asthma. The mechanism of effect of nedocromil, often prescribed in children, has been discussed. Our previous study on the effect of nedocromil on different inflammatory markers, showed decreased levels of IL-4 and IgE after monotherapy in 15 asthmatic children. The purpose of this study was to define the effect of treatment with nedocromil on serum level of IL-4 and IgE, clinical symptoms and bronchial hyperreactivity (BHR) in children with moderate atopic asthma. It was 8 week, placebo-controlled and randomized, double blind trial of 81 children with moderate atopic asthma allergic to dust mite. Patients were randomly allocated to receive nedocromil sodium two puffs four times daily (0.002 g/puff) (n = 34) or placebo (n = 47). 69 children completed the study. After treatment with nedocromil the levels of IL-4 and IgE in blood serum in study group significantly decreased, and all clinical parameters improved. Mean levels of IL-4 in serum before and after treatment with nedocromil were 0.13 pg/ml +/- 0.01 and 0.12 pg/ml +/- 0.02 respectively (p < 0.01). Mean serum levels of IgE before and after treatment with nedocromil were 556.83 IU/ml +/- 201.3 and 485 IU/ml +/- 200.5 respectively (p < 0.02). This study demonstrate that one possible way by which nedocromil contribute to inhibition of allergic inflammation is by decreasing IL-4 and IgE levels.