Human mast cells and basophils are conventionally considered primary effector cells of bronchial asthma. There is now compelling evidence that these cells differ immunologically, biochemically and pharmacologically, which suggests that they might have distinct roles in the appearance and fluctuation of the asthma phenotype. Recent data reveal the complexity of the roles of human mast cells and basophils in asthma and have shed light on the control of recruitment and activation of these cells in different lung compartments. Preliminary evidence suggests that these cells might not always be detrimental in asthma but, under some circumstances, have a protective role in modulating certain aspects of innate and acquired immunity and allergic inflammation.