Since thymic factor activity can modulate immunoglobulin production, thymomodulin effect on IgE secretion was studied in thirty children (20 atopic and 10 control patients). Before treatment circadian variability of IgE was verified in all the children. Thymomodulin (3 mg/kg/die) was given daily for 30 days in both groups. Disappearance of circadian IgE variability were observed in atopic children, while no change of serum IgE circadian levels occurred in control group. On the basis of our results an improvement of IgE disregulation in atopic children may be postulated.