In guinea pigs sensitized with ovalbumin the respiratory epithelium lost its ability to modulate the responses of airway smooth muscles to histaminergic stimuli. Incubation of bronchial segments with IL-5 potentiated the contractile responses of bronchial smooth muscles to histamine in both intact and sensitized animals. Incubation of bronchial segments with IL-5 receptors moderated contractile activity of segments from sensitized pigs, but not in the segments from intact controls.