Interleukin 4, (IL4) known as a lymphokine secreted by type II helper T-cells, is thought to regulate IgG and IgE secretions. Therefore, elevated IL4 levels are expected in atopic allergic disease and parasitoses. The purpose of this study was to determine IL 4 levels in allergic asthmatic children. In 50 extrinsic atopic children (19 females, 31 males, mean age 8 +/- 4), IgE and IL 4 were found to be 469 +/- 296 U/L and 0.318 +/- 0.09 ng/ml, respectively. In seven control cases, IgE and IL4 levels were 62 +/- 25 and 0.106 +/- 0.017, respectively. Comparison of the two groups disclosed statistically significant differences in IL4 and IgE levels, suggesting the ability of IL4 to augment IgE production.